The research, led by Fei Yu and corresponding author Shujing Li, focuses on a deceptively simple question: what happens when you swap the binder that holds an insulation fiberboard together? The team fabricated inorganic fiber-based insulation boards using mechanical compression molding, a process in which fibers and a liquid binder are pressed into a dense, coherent body. They systematically compared two of the most common sol-gel binders in the refractory world, silica sol and alumina sol, and then went a step further by blending the two in varying ratios to see whether the strengths of each could be captured in a single material.

The results are striking. Boards bonded with alumina sol showed dramatically enhanced mechanical performance at room temperature, with compressive strength increases ranging from 74.6 percent to 331.0 percent compared with boards bonded with silica sol. That is not an incremental improvement; in some formulations it means a board that can carry more than four times the load before crushing. For manufacturers of insulation panels, which must survive handling, stacking, machining, and installation without crumbling, such a leap in green and finished strength could translate directly into lower breakage rates, thinner support structures, and more design freedom.

But there is no free lunch in high-temperature materials. The same alumina-bonded boards that shrugged off mechanical loads at ambient conditions showed reduced stability and poorer thermal insulation performance when the temperature climbed. The underlying reasons trace back to how each sol behaves during drying and heating. Silica sol, a colloidal suspension of amorphous silica nanoparticles, gels into a network that preserves porosity and resists the densification and shrinkage that degrade insulation at high temperature. Alumina sol, by contrast, forms bonding bridges that lock fibers together far more effectively at room temperature, but the resulting microstructure evolves differently under heat, compromising the board’s ability to resist shrinkage and maintain its insulating pore network in service.

This tension between mechanical integrity and thermal performance is the central challenge the authors identify. Insulation boards work by trapping air in a labyrinth of fine pores between fibers; anything that collapses those pores, or that introduces phases which sinter or crystallize aggressively at operating temperature, erodes the material’s function. At the same time, a board with insufficient binder simply falls apart before it ever reaches a furnace. Achieving an optimal balance between room-temperature mechanical integrity and high-temperature insulation performance remains, as the team puts it, a critical challenge, particularly when selecting suitable binder systems.

The elegant part of the study lies in its exploration of mixed sol systems. By blending alumina and silica sols in controlled ratios, the researchers created hybrid binders whose boards partially integrate the complementary advantages of both components. As the alumina sol content in the hybrid system increases, the microstructure and overall performance of the fiberboards progressively approach those of the pure alumina system. In other words, the two binders do not merely average their properties; the mixture behaves in a predictable, tunable way that follows the composition. This gives engineers something rare in refractory materials: a continuous dial rather than a binary choice.

The practical implications of that dial are considerable. A steel plant lining a ladle wall might prioritize high-temperature stability and low thermal conductivity, favoring a silica-rich formulation. A manufacturer producing insulation modules that must be shipped across the country and bolted into place might accept somewhat reduced high-temperature performance in exchange for boards that survive transport without cracking, favoring a higher alumina fraction. Between those extremes lies a spectrum of compositions, each with a characteristic balance of strength, shrinkage resistance, and insulating capacity. The study establishes that tailoring the type and proportion of composite sol enables directional property design for fiberboards, providing a viable strategy to meet specific application requirements across diverse thermal environments.

The scientific context makes the work more than a recipe book. Silica sols have long served as refractory fiber binders, valued for forming stable siloxane networks on heating, while alumina sols have gained attention for their ability to bond high-alumina refractory castables and promote strong ceramic bridges between particles and fibers. Sol-gel processing itself, in which colloidal oxide nanoparticles are dispersed in liquid and gelled in place, allows binders to be deposited at the nanoscale precisely where fibers touch, maximizing bonding efficiency with minimal added mass. The Wuhan team’s contribution is to bring these two binder chemistries into direct, systematic comparison within the same fiber system and molding process, eliminating the confounding variables that make cross-study comparisons unreliable.

The work also connects to a broader push toward energy-efficient thermal materials. Lightweight porous ceramics, fiber aerogels, and foam-gelcast structures are all racing to push thermal conductivity lower while maintaining mechanical robustness, driven by industrial decarbonization and the demands of hypersonic flight and next-generation energy systems. Fiberboards occupy a crucial niche in this landscape because they are cheap, scalable, and easy to fabricate into large panels, but their performance ceiling is set by the binder. A binder strategy that can be tuned composition by composition, as this study demonstrates, effectively raises that ceiling without requiring new fiber chemistries or exotic processing equipment.

For now, the message of the research is one of controlled compromise rather than miracle materials. Alumina sol delivers exceptional room-temperature strength at a documented cost in high-temperature performance; silica sol preserves thermal function but leaves boards mechanically fragile; and mixed sols occupy the ground in between in a predictable, designable way. The team, supported by the National Natural Science Foundation of China and Hubei provincial research funds, has provided the quantitative map that lets engineers navigate that compromise deliberately. In a field where binder selection has often been guided by habit and trial, the ability to choose a sol ratio and know, in advance, roughly where the resulting board will land on the strength-insulation spectrum is a quiet but meaningful advance for the materials that keep the hottest machines on Earth running safely.

Subject of Research: Sol binder selection and mixing for thermal insulation fiber composites

Article Title: Preparation, performance and underlying mechanisms of single and mixed sols in thermal insulation fiber composites

Article References: Preparation, performance and underlying mechanisms of single and mixed sols in thermal insulation fiber composites. (n.d.). https://doi.org/10.1007/s10853-026-13867-6

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13867-6

Keywords: silica sol, alumina sol, thermal insulation, fiber composites, ceramic fiberboards, binders, compressive strength, high-temperature materials, sol-gel, porous materials, refractories, mechanical compression molding

The star of the study is polyolefin elastomer, or POE, a flexible ethylene-octene copolymer that has become a favorite candidate for cushioning applications because it is soft, tough, and relatively inexpensive. POE foams, however, have a stubborn weakness: their melt strength is limited. When a molten sheet of POE is foamed, the growing gas bubbles, or cells, can merge with one another in a process called coalescence, and the resulting cellular structure can collapse or shrink after foaming. The result is an unstable foam with poor dimensional stability and disappointing mechanical performance. To combat this, the researchers turned to a two-pronged strategy: chemical crosslinking to stiffen the polymer network, and blending in a second elastomer, olefin block copolymer, or OBC, to reinforce the melt and refine the cell structure.

The chemistry behind the crosslinking step is straightforward but consequential. The team added 0.9 parts per hundred resin of bis(1-(tert-butylperoxy)-1-methylethyl)benzene, known in the trade as BIPB, a peroxide that decomposes under heat and generates free radicals. These radicals abstract hydrogen atoms from the polymer chains, creating chain radicals that couple with one another to form covalent crosslinks. The crosslinked network behaves like a molecular scaffolding: during foaming it holds the expanding melt together, preventing neighboring cells from rupturing and merging. The researchers confirmed the extent of crosslinking by measuring the xylene-insoluble fraction, the portion of the material that will not dissolve in hot solvent because it is tied into a network. As OBC content rose from zero to 50 parts per hundred resin, this insoluble fraction climbed from 82.2 percent to 90.9 percent, a clear sign that the blend was forming a progressively denser crosslinked architecture.

The OBC itself is a fascinating material. Produced by chain-shuttling polymerization, it consists of alternating blocks of crystallizable ethylene-octene sequences and amorphous octene-rich segments. The hard crystalline blocks act as physical crosslinks that melt at elevated temperature, while the soft amorphous blocks provide elasticity. In the POE/OBC blends, the OBC increased both the storage modulus and the complex viscosity of the melt, exactly the rheological changes that stabilize growing bubbles. At the same time, the overall apparent crystallinity of the composites dropped dramatically, from 18.1 percent down to 7.3 percent as OBC loading increased. This reduction in crystallinity matters for foaming because crystals can act as nucleation sites and also stiffen the matrix; less crystallinity means a softer, more deformable cell wall that can stretch further before failing.

With the materials in hand, the team employed supercritical carbon dioxide foaming, a technique that has become the gold standard for environmentally friendly polymer foam production. In this process, the polymer is saturated with carbon dioxide pressurized above its critical point, where the gas takes on liquid-like density and gas-like diffusivity, allowing it to dissolve into the polymer in large quantities. When the pressure is released or the temperature is raised, the dissolved gas comes out of solution and nucleates billions of tiny bubbles. Because carbon dioxide is nontoxic, nonflammable, and leaves no residue, the method avoids the ozone-depleting and greenhouse-active blowing agents that older foam processes relied on. The researchers selected foaming conditions of 100 degrees Celsius and 15 megapascals, a window where the crosslinked blends could expand uniformly without collapsing.

The foaming results revealed a composition-dependent balancing act. The formulation containing 20 parts per hundred resin of OBC, designated F-OBC-20, achieved the highest volume expansion ratio of the series, reaching 8.90 plus or minus 0.13, meaning the foam swelled to nearly nine times the volume of the original solid. At the other end of the spectrum, the formulation with 50 parts of OBC, F-OBC-50, produced the finest cellular architecture: an average cell size of just 54.3 plus or minus 5.1 micrometers and an extraordinary cell density of 1.66 times ten to the seventh cells per cubic centimeter. These microcellular structures are prized because smaller, more numerous cells distribute stress more evenly and trap gas more effectively, improving both mechanical performance and insulation.

The functional payoffs were substantial. Ball rebound resilience, a standard measure of how much energy a foam returns after an impact, increased from approximately 31 percent for the base formulation to over 43 percent for the OBC-rich composites. That improvement translates directly into cushioning materials that feel springier and recover their shape more completely after repeated compression, a property that matters enormously in footwear midsoles and sports protective equipment. Simultaneously, the thermal conductivity of the foams fell from 0.0819 to 0.0607 watts per meter-kelvin, a roughly 26 percent reduction. Lower thermal conductivity means better insulation, and the finer cells of the high-OBC foams contribute by suppressing convection and radiation within the cellular structure while the polymer itself conducts less heat.

Not every property moved in a favorable direction, and the authors are candid about the trade-offs. The specific compressive stress at 50 percent strain, which measures the load-bearing capability of the foam normalized by its density, decreased as OBC content rose. In other words, the bouncier, better-insulating foams were somewhat softer under sustained compression. This is the classic dilemma of foam design: expansion, cellular refinement, resilience, insulation, and compressive strength do not all improve together at a fixed crosslinker loading. The value of the study lies precisely in quantifying these trade-offs, giving manufacturers a data-driven basis for choosing a formulation that matches a specific application, whether that is a shoe midsole that prioritizes energy return or an insulation panel that prioritizes low thermal conductivity.

The broader significance of the work extends beyond the specific POE/OBC system. Supercritical carbon dioxide foaming is rapidly becoming the preferred route for thermoplastic and elastomeric foams across the industry, and studies like this one show how molecular design, crosslinking chemistry, and process conditions can be orchestrated together to overcome the intrinsic limitations of a given polymer. The Beijing team’s approach of using a block copolymer to simultaneously boost melt strength, refine cells, and enhance elasticity could inspire similar strategies in other elastomer families, from thermoplastic polyurethanes to poly(ether-block-amide)s, where shrinkage and cell instability have long frustrated foam producers.

For consumers, the research points toward a future in which the foam inside a sneaker, a yoga mat, or a building panel is lighter, springier, and more insulating than what is available today, all manufactured with a benign gas instead of legacy chemical blowing agents. For the polymer science community, the study provides a rigorous, quantitative demonstration that composition is a powerful lever: by simply adjusting the ratio of two compatible olefin elastomers while holding the peroxide crosslinker constant, the researchers swept across a wide property space, from high-expansion foams to microcellular insulators. As demand grows for sustainable, high-performance cellular materials, that kind of precise compositional control may prove to be the difference between a foam that fails in service and one that endures.

Subject of Research: Supercritical CO2 foaming of crosslinked POE/OBC elastomer composites for enhanced foam resilience and thermal insulation

Article Title: Supercritical CO2 foaming of POE/OBC composite foams with enhanced resilience and thermal insulation

Article References: Supercritical CO2 foaming of POE/OBC composite foams with enhanced resilience and thermal insulation. (n.d.). https://doi.org/10.1007/s00289-026-06700-2

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06700-2

Keywords: polyolefin elastomer, olefin block copolymer, supercritical CO2 foaming, polymer foams, crosslinking, BIPB peroxide, resilience, thermal insulation, cell morphology, melt strength, cushioning materials, Polymer Bulletin

The new composite, designated CNGA, is described in the journal Advanced Composites and Hybrid Materials. Rather than packing conductive carbon into a block, the team assembled the material through heterogeneous ice-templated freeze casting, a process in which growing ice crystals sculpt the internal architecture as the suspension solidifies. The result is a hierarchical porous structure in which double-shell hollow microspheres are spatially segmented and joined by controllable bridges of nitrogen-doped carbon nanosheets. Each microsphere and each bridge plays a distinct electromagnetic role, and because the geometry is imposed during assembly rather than left to chance, the balance between attenuation and impedance matching can be tuned deliberately.

The physics behind the approach is subtle but crucial. When an electromagnetic wave strikes a material, two things must happen for effective absorption. First, the wave has to enter rather than reflect away, which requires the material’s impedance to match that of free space. Second, once inside, the wave’s energy has to be dissipated, typically through dielectric polarization, conduction losses, and magnetic losses. Highly conductive fillers are excellent dissipators but terrible reflectors, bouncing incoming waves off the surface. The distributed RLC framework tackles this by separating the two jobs: the carbon nanosheet bridges provide continuous conductive pathways for energy dissipation, while the spatially distributed hollow microspheres introduce a wealth of heterogeneous interfaces that localize electromagnetic loss without overloading the material with conductivity.

The microspheres themselves are engineered for complexity. Each carries a double shell, and their hollow interiors lower the overall density while multiplying the number of internal boundaries at which electromagnetic waves can be reflected, scattered, and attenuated. Nitrogen doping, in the form of pyridinic and pyrrolic nitrogen sites within the carbon lattice, enhances polarization losses by creating defect-rich sites that trap charge under an oscillating electromagnetic field. Meanwhile, nickel-induced graphitization converts regions of amorphous carbon into more ordered graphitic domains, boosting conduction losses. The two mechanisms act in concert, giving the material multiple channels through which microwave energy can be converted into heat.

The measured performance is striking by any standard. The optimized aerogel achieves a reflection loss of –54.86 decibels, meaning that at the absorption peak, only a vanishingly small fraction of the incoming microwave energy is reflected back toward the source. In practical terms, that is deep into the regime prized for radar absorption, where the power of a returned signal is cut by many orders of magnitude. Equally important, the effective absorption bandwidth—the frequency range over which the material reflects at least 90 percent of incident energy—spans 6.56 gigahertz, covering a broad swath of the microwave spectrum rather than a single narrow band.

What makes these numbers especially notable is the filler loading at which they are achieved: only 8 weight percent. In conventional microwave absorbers, achieving comparable performance often requires loading a matrix with 40 to 70 percent functional filler, which drives up weight and can embrittle the composite. A low loading is essential for aerospace platforms, where every gram matters, and for electronics, where thick or heavy shielding layers are unwelcome. The lightweight aerogel also delivers thermal insulation, with a thermal conductivity of just 0.0605 watts per meter-kelvin, comparable to some of the best commercial insulating foams, and an infrared absorptivity exceeding 95 percent.

The thermal behavior is a direct consequence of the architecture. The hollow interiors and hierarchical porosity mean that heat must navigate a tortuous, largely air-filled path through the material, and air is a notoriously poor thermal conductor. Infrared radiation, meanwhile, is absorbed efficiently across the extended surfaces of the carbon components. This combination means the aerogel can simultaneously suppress heat flow and swallow radiant heat, which matters for applications ranging from protecting sensitive electronics from thermal gradients to managing temperature in aircraft structures where hot and cold zones sit close together.

Mechanical robustness, often the weak point of ultralight aerogels, received its own fix. As-synthesized porous carbon architectures tend to be fragile, but the team found that infiltrating the aerogel with resin raised its compressive strength to 45.70 megapascals without degrading electromagnetic performance. The resin fills the load-bearing framework without disrupting the conductive pathways or the interface density that underpins the wave absorption, turning an admittedly delicate laboratory material into something with realistic prospects for structural use. That step matters because a multifunctional material is only useful if it can survive handling, vibration, and compression in service.

The broader significance of the work lies in its structural philosophy. Instead of optimizing one property at a time and accepting compromises elsewhere, the researchers treated the composite as a spatially regulated system in which geometry, composition, and connectivity are co-designed. The segmentation of the microspheres controls where heterogeneous interfaces appear; the controllable connection of the carbon bridges sets the conductivity of the network; and the ice-templating process allows both to be patterned simultaneously. This structure–property strategy offers a template that other teams can apply to different material chemistries, potentially extending the distributed RLC concept to absorbers that operate in other frequency bands or that combine additional functions such as sensing or mechanical damping.

The work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, and two state key laboratories, reflecting the strategic weight placed on electromagnetic compatibility and thermal management in next-generation technology. As wireless devices proliferate and stealth, radar-cross-section management, and high-frequency electronics demand ever better absorbers, materials that swallow microwaves, block heat, and carry mechanical load in a single lightweight layer will only grow more valuable. The CNGA aerogel is a demonstration that, with the right architecture, the classic trade-off between dissipation and impedance matching can be engineered away rather than merely tolerated.

Subject of Research: Hierarchical hollow microsphere-carbon composite aerogels for electromagnetic wave absorption and thermal regulation

Article Title: Spatial segmentation and controllable connection enabled hollow microsphere-carbon distributed RLC networks for multifunctional EM/thermal regulation

Article References: Spatial segmentation and controllable connection enabled hollow microsphere-carbon distributed RLC networks for multifunctional EM/thermal regulation. (n.d.). https://doi.org/10.1007/s42114-026-02073-2

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02073-2

Keywords: electromagnetic wave absorption, microwave absorbers, hollow microspheres, carbon nanosheets, aerogels, thermal insulation, impedance matching, nitrogen doping, ice-templated assembly, RLC networks, lightweight composites, mechanical reinforcement

The team began with balsa wood, a precursor prized for its very low density of roughly 0.1 grams per cubic centimeter, high porosity, and well-defined anatomical anisotropy. Natural wood is anything but uniform: its axial direction runs parallel to tree growth and exposes honeycomb-like cellular channels, its radial direction reveals the extended planar surfaces of wood ray lamellae, and its tangential direction presents a more homogeneous network punctuated by lenticular ray cross-sections. Previous studies of wood-derived carbon absorbers had largely confined their measurements to a single direction, leaving the link between this inherent structure and electromagnetic response poorly understood. The new work set out to establish that structure–electromagnetic correlation directly.

To fabricate the material, the researchers first delignified the wood using an acidified sodium chlorite treatment, removing lignin and part of the hemicellulose, then freeze-dried the result to obtain a wood sponge. Carbonization at 680 degrees Celsius under flowing argon produced the wood carbon sponge, a structure just 0.035 grams per cubic centimeter in density. During freezing, ice crystals preferentially nucleated in the water-rich wood rays, expanding and compressing neighboring fiber cells until the honeycomb pores closed, generating an undulating, arch-shaped lamellar architecture. The carbon sponge was then impregnated under vacuum with a methyltrimethoxysilane-derived organosilica sol, gelled, aged, solvent-exchanged, and dried at ambient pressure, yielding the composite, which rises to about 0.13 grams per cubic centimeter but fully preserves the anisotropic skeleton, with silica nanoparticles uniformly filling the interlayer voids.

An extensive characterization campaign confirmed the design. Scanning electron microscopy revealed the distinct lamellar, fused-fiber, and ray-lamellae structures along the three anatomical axes, while three-dimensional micro-CT showed homogeneous dispersion of the organosilica phase across the entire millimeter-scale monolith. Nitrogen adsorption and mercury intrusion porosimetry showed that the pure carbon sponge is dominated by micropores around 2 nanometers formed during pyrolysis, whereas the composite develops a broad mesoporous network spanning roughly 2 to 100 nanometers. Infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy together tracked the removal of lignin, the conversion of cellulose into partially graphitized amorphous carbon, and the successful incorporation of the silica network through characteristic Si–O–Si and Si–CH3 signatures.

Electromagnetic testing over 2 to 18 gigahertz using the coaxial transmission line method exposed a robust directional ordering: complex permittivity was consistently highest in the tangential direction, intermediate in the radial direction, and lowest in the axial direction. In the tangential orientation, the electric field drives charge carriers unimpeded along continuous conductive lamellar planes, producing an overdeveloped conductive network, severe impedance mismatch, and an interface reflection coefficient approaching 39 percent at 2 gigahertz. Along the axial direction, charge transport is repeatedly interrupted by interlayer interfaces, so conductivity and dielectric loss are low even though waves enter easily. The radial direction proved the sweet spot: the undulating, arch-shaped lamellae force incident waves through multiple internal reflections and scattering, prolonging propagation paths and creating abundant polarization sites without forming an overly continuous conductive network.

The silica aerogel played a dual regulatory role. Acting as a low-permittivity phase, it diluted and partially disrupted the excessive conductive network, shifting impedance matching toward the ideal range in all three directions. Simultaneously, the newly created carbon/silica heterogeneous interfaces served as additional polarization centers, intensifying interfacial polarization relaxation and boosting dielectric loss. The results were striking: the composite’s tangential direction, previously the worst absorber, achieved a minimum reflection loss of −64.1 decibels at a thickness of 3.15 millimeters, while the radial direction delivered an effective absorption bandwidth of 11.6 gigahertz at only 4.95 millimeters of thickness, fully covering the X and Ku bands and outperforming most reported carbon aerogels.

Quantitative analysis based on Debye relaxation theory separated the dielectric loss into conduction and polarization components, confirming these interpretations. Cole–Cole plots showed that the pure sponge’s tangential direction was dominated by polarization loss from surface charge accumulation, while the radial and axial directions were conduction-dominated at low frequencies and increasingly polarization-driven at higher frequencies. After silica incorporation, the polarization-to-conduction loss ratio rose in the radial and axial directions, reflecting the new heterogeneous interfaces and dipole sites, while falling in the tangential direction as alleviated impedance mismatch allowed interior conductive networks to be activated. A quarter-wavelength interference model further showed that absorption peaks aligned precisely with theoretical matching thicknesses, validating the underlying cancellation mechanism. Radar cross-section simulations on coated metal plates indicated that the composite in the tangential orientation kept monostatic radar signatures below −10 decibel square meters across angles from −80 to 80 degrees, underscoring its practical stealth potential.

Beyond electromagnetic performance, the composite excelled as a thermal insulator and a resilient mechanical structure. Thermal conductivity dropped from 0.054, 0.048, and 0.044 watts per meter-kelvin in the axial, radial, and tangential directions of the pure sponge to 0.040, 0.038, and 0.037 watts per meter-kelvin in the composite, with the nanoporous silica network suppressing gas conduction through the Knudsen effect and forcing heat along tortuous solid pathways. Placed on a 150-degree-Celsius hot stage, the tangential face of the composite rose only to 32.2 degrees Celsius after five minutes. Mechanically, the tangential direction behaved elastically, sustaining 50 percent strain, and after silica reinforcement it carried 419 kilopascals at that strain, roughly ten times the unreinforced value. After 50 loading-unloading cycles at 50 percent strain, the sample retained 92.3 percent of its height with stable energy dissipation, evidence of durable compressibility and resilience.

The broader significance of the work lies in its demonstration that nature’s own architecture can serve as a design parameter rather than a limitation. By preserving and exploiting the anisotropic cellular structure of wood, and then tuning it with a judiciously chosen dielectric filler, the researchers showed that electromagnetic, thermal, and mechanical responses can be engineered simultaneously and selected direction by direction according to application needs. The tangential orientation offers the best thermal insulation and mechanical compliance, the radial orientation delivers unmatched broadband absorption, and the axial orientation provides easy wave entry with moderate loss. This application-oriented customization points toward a new generation of lightweight, sustainable, multifunctional composites for radar stealth, electromagnetic compatibility, and thermal protection, all rooted in one of humanity’s oldest and most renewable materials.

Subject of Research: Wood carbon sponge/silica aerogel composites with anisotropic broadband microwave absorption, elastic resilience, and thermal insulation

Article Title: Wood Carbon Sponge/SiO2 Aerogel Composites with Anisotropic Broadband Microwave Absorption, Elastic Resilience, and Thermal Insulation

Article References: Wood Carbon Sponge/SiO2 Aerogel Composites with Anisotropic Broadband Microwave Absorption, Elastic Resilience, and Thermal Insulation. (n.d.). https://doi.org/10.1002/advs.77888

Image Credits: AI Generated

DOI: 10.1002/advs.77888

Keywords: wood carbon sponge, silica aerogel, microwave absorption, anisotropic materials, biomass-derived carbon, thermal insulation, radar stealth, impedance matching, interfacial polarization, balsa wood, carbon aerogel, lightweight composites

The new material belongs to a family of compounds known as two-dimensional hybrid organic-inorganic perovskites. These are layered semiconductors in which alternating sheets of organic and inorganic components stack into a highly ordered crystalline structure. The inorganic layers provide mechanical rigidity and structural definition, while the organic layers act as spacers whose chemical composition can be tuned almost at will. That tunability is the key to the new result. In their earlier work, the NC State team had already observed unusual combinations of stiffness and thermal behavior in this class of materials, but the new study represents a deliberate, targeted effort at molecular engineering rather than an incidental discovery.

The specific strategy involved modifying the carbon-carbon chains within the organic layers. By replacing a portion of those chains with a carefully tailored combination of benzene rings, the researchers gained precise control over how the material conducts heat and how rigid it is. Benzene rings are bulky, planar molecular units that disrupt the efficient pathways along which vibrational energy, and therefore heat, normally travels through a solid. Incorporating them in a controlled way scatters the lattice vibrations, known as phonons, that would otherwise carry thermal energy across the layers, while the overall layered architecture preserves the crystalline order that gives the film its stiffness.

The material the team produced is an azobenzene ethyl ammonium lead iodide thin film. When tested at room temperature, it exhibited a thermal conductivity of approximately 0.04 watts per meter-kelvin. To appreciate how remarkable that figure is, consider silicone, a soft polymer widely used to insulate against heat in everyday products such as oven mitts. Silicone has a thermal conductivity of about 0.2 watts per meter-kelvin, five times higher than the new perovskite film. Yet the engineered film is not a squishy insulating gel; it is a rigid semiconductor with mechanical stiffness exceeding that of silicone by a factor of roughly 700 to 10,000, depending on how the comparison is made. Combining those two figures underscores the scale of the achievement: a dense, load-bearing material that insulates better than the soft foams and elastomers engineers usually reach for when heat control matters.

Dali Sun, co-corresponding author of the study and a professor of physics at NC State, emphasizes why this combination is so valuable. Stiff materials that are good thermal insulators would have substantial utility across a wide range of applications, from cookware to electronic devices to space travel, he notes. The problem, he explains, is that in general stiff materials conduct heat well, and materials that insulate well are not stiff. The new compound is very stiff and extremely good at insulating against heat, outperforming any material one would find in nature. That framing is not marketing hyperbole but a statement about the material’s position relative to the entire known landscape of dense solids.

Jun Liu, co-corresponding author and an associate professor of mechanical and aerospace engineering at NC State, describes the work as a demonstration of what advanced molecular engineering can achieve when properties are designed intentionally rather than accepted as given. The team had previously demonstrated unusual behavior related to the combination of stiffness and thermal conductivity in a specific class of materials, she says, and for this study they engaged in more advanced molecular engineering to deliberately create an extreme combination of those properties. The result approaches the theoretical floor for thermal conductivity in a non-porous solid, meaning there is very little room left for any conventional material to do better without introducing porosity, which would sacrifice stiffness and structural integrity.

Equally important for practical adoption is the fact that the production method scales. Liu notes that the technique used to create the film can be scaled up fairly easily, allowing the material to be produced at fairly large scales, applied as a coating, and integrated into existing manufacturing workflows. This is a critical distinction from many laboratory-record thermal insulators, such as exotic aerogels or nanostructured ceramics, which achieve impressive numbers only through porous architectures that are difficult to produce uniformly over large areas and which lack the mechanical strength needed for demanding applications. A printable thin film that is both stiff and ultrainsulating opens the door to conformal thermal barriers on electronic components, protective layers in high-temperature environments, and insulation systems for aerospace structures where every gram and every millimeter counts.

The study, titled Extremely Low Thermal Conductivity in Rigid Layered Hybrid Perovskites, was published on September 18, 2026, in Science Advances. Co-lead authors are Ziqi Wang and Ankit Negi, Ph.D. graduates of NC State, along with Liang Yan of the University of North Carolina at Chapel Hill and Qingxuan Wang of Nanjing Normal University. The co-corresponding authors are Jun Liu and Dali Sun of NC State, Wei You of UNC Chapel Hill, and Jun Zhou of Nanjing Normal University. The broader author team includes contributors from NC State, UNC Chapel Hill, Texas A&M University, Yale University, Shanghai Polytechnic University, and Wenzhou University, reflecting the collaborative experimental and computational effort required to synthesize, characterize, and model the material’s behavior.

The research was supported by the National Science Foundation under multiple grants, by the U.S. Department of Energy, by the Office of Naval Research, and by the Goodnight Innovation Distinguished Professor Endowment. Beyond the specific compound, the authors point to the broader significance of the work: it highlights the potential of molecular engineering to fine-tune hybrid layered materials for applications that require novel combinations of stiffness and thermal insulation. If the same benzene-ring design principle can be extended across other members of the hybrid perovskite family and into related layered systems, the coming years could see a new generation of structural materials in which heat management is designed into the molecular architecture itself rather than bolted on afterwards. For engineers designing everything from smartphone processors to spacecraft heat shields, that prospect transforms thermal insulation from a compromise into a design variable.

Subject of Research: Development of a rigid two-dimensional hybrid organic-inorganic perovskite thin film with extremely low thermal conductivity achieved through molecular engineering of organic layers.

Article Title: New thermal insulator outperforms any material found in nature

Article References: New thermal insulator outperforms any material found in nature. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: thermal insulation, hybrid perovskites, molecular engineering, thin films, thermal conductivity, materials science, NC State University, Science Advances, stiffness, phonon scattering, benzene rings, thermal barriers