Porous Boron Nitride Membrane Keeps Skin Cool and Breathable in One Step

Wearable electronics have a persistent problem that has little to do with chips or batteries: the skin underneath them gets hot, sweaty, and uncomfortable. Materials that sit against the body for hours need to let moisture vapor escape, dissipate heat away from the interface, and flex with every movement, all at once. In practice, engineers have usually had to pick two of those three properties and sacrifice the third. Soft elastomers conform beautifully but trap heat and sweat. Highly porous fabrics breathe well but conduct heat poorly, because still air is one of the worst thermal conductors known. A research team in South Korea now reports a way out of that trade-off, using a remarkably simple manufacturing trick that builds breathability and heat-spreading ability into the same thin membrane in a single step.

The study, published in the journal Advanced Composites and Hybrid Materials, describes a porous composite membrane made from hexagonal boron nitride (hBN) nanoplatelets embedded in polydimethylsiloxane (PDMS), the soft silicone elastomer that dominates skin-wearable design. The key innovation lies in how the pores are created. Instead of templating, washing, solvent extraction, or any post-fabrication treatment, the researchers mixed a volatile liquid, perfluorohexane (PFH), directly into the hBN/PDMS formulation. As the membrane was cast and cured, the PFH evaporated on its own, leaving behind a stable network of air voids. The porous architecture emerges during curing itself, which means the process can in principle run as a continuous, one-step casting operation without extra processing stages that add cost and complexity.

What makes the approach more than a convenience is the degree of control it offers. The team found that pore size could be tuned simply by changing the curing temperature, because temperature governs a kinetic race between two competing processes: the solidification of the PDMS matrix and the volatilization of the PFH porogen. When curing outpaces evaporation, the growing polymer locks in a particular pore morphology; when evaporation dominates, the voids evolve differently. By adjusting this balance, the researchers could dial in the porous structure without changing the chemistry of the formulation. Meanwhile, the overall porosity of the membrane rose from roughly 15 percent to about 31 percent as the PFH content in the mixture increased, giving a second, independent handle on the material’s internal architecture.

The central surprise of the work is thermal. Porosity normally kills thermal conductivity, since air-filled voids interrupt the paths along which heat travels. Yet the porous hBN/PDMS membrane achieved a thermal conductivity of 0.22 watts per meter-kelvin, essentially matching the dense form of the same composite. The explanation lies in how the hBN nanoplatelets arrange themselves during fabrication. Rather than being distributed randomly through the bulk, the platelets assemble along the walls of the pores, forming continuous heat-conduction pathways that thread through the material. Heat entering the membrane finds an interconnected skeleton of thermally conductive boron nitride to follow, even as the voids between those pathways remain open for water vapor transport. Breathability and heat dissipation, usually opposing goals, are satisfied simultaneously by the same microstructure.

To understand this behavior in more detail, the researchers turned to computational fluid dynamics simulations. The modeling showed that heat is transferred more effectively near the interface between the hBN and the PDMS matrix in the porous membrane than in comparable dense structures. That computational picture matched what the team observed experimentally: the porous membrane accumulated less heat during use. In a skin-interface application, lower heat accumulation translates directly into less thermal stress on the tissue beneath, which matters both for user comfort and for the accuracy of sensors that measure physiological signals through the skin.

Thermal performance alone would not make a material suitable for wear. The team therefore evaluated the membrane in contact with living skin. In vivo analysis showed that the porous membrane kept skin hydration at a stable level of approximately 103 to 107 percent over the testing period, indicating that the material does not trap moisture against the skin or dry it out. Hydration stability is a meaningful benchmark for wearables, because occlusive films that block vapor transport cause the skin to macerate over time, degrading both comfort and measurement quality. A membrane that holds hydration in a narrow, healthy band addresses one of the most common complaints about long-duration skin patches.

Mechanical compliance proved equally convincing. The porous membrane’s mechanical behavior was found to be close to that of bare skin, meaning the material deforms in a way that the body does not register as a stiff foreign object. This is where the choice of PDMS as the matrix pays off: the elastomer is soft, stretchable, and biocompatible, and introducing controlled porosity pushes its effective stiffness even lower. Combined with the hydration results, the mechanical data suggest that the membrane satisfies both the physiological and mechanical criteria for comfortable, extended skin contact, which the authors describe as the foundation for future skin-interface applications.

The significance of the work extends beyond a single material recipe. Hexagonal boron nitride is prized in electronics for its thermal conductivity, electrical insulation, and chemical stability, and pairing it with PDMS is a natural strategy for thermally managed wearables. What has been missing is a fabrication route that preserves those thermal benefits while adding breathability without extra processing. By using a volatile porogen that does its job and disappears during curing, the researchers have effectively turned the manufacturing step itself into the design tool. The pore structure, the porosity, and the platelet alignment all emerge from the interplay of curing kinetics and evaporation, parameters that are easy to adjust on a production line.

The study was a collaboration between the Research and Innovation Center of Amorepacific Corporation in Yongin and the School of Mechanical Engineering at Soongsil University in Seoul, combining industrial materials expertise with mechanical engineering analysis. The work was supported by South Korea’s National Research Foundation through its Bio and Medical Technology Development Program and the G-LAMP Program, as well as by the Ministry of Trade, Industry and Energy through an Industrial Technology Innovation Program grant. The involvement of a major cosmetics and personal care company hints at near-term applications in skin patches, cosmetic films, and health-monitoring wearables, where thermal comfort and moisture management directly affect product performance.

For the wearable industry, the message is that the long-standing trade-off between breathability and thermal management may be an artifact of how porous materials have been made, not a law of physics. If thermally conductive fillers can be guided to line the pore walls of a soft elastomer, air voids no longer have to be thermal dead ends. The one-step PFH porogen method offers a scalable route to that architecture, with tunable pores, no washing or extraction stages, and demonstrated comfort on living skin. As skin-interfaced sensors, electronic skins, and on-body therapeutic devices multiply, materials like this porous hBN/PDMS membrane could determine whether the next generation of wearables is something people actually forget they are wearing.

Subject of Research: One-step fabrication of porous hexagonal boron nitride/PDMS composite membranes for breathable, thermally dissipative skin-interface wearable applications

Article Title: One-step fabrication of a porous hBN/PDMS composite membrane for breathable and thermally dissipative skin-interface applications

Article References: One-step fabrication of a porous hBN/PDMS composite membrane for breathable and thermally dissipative skin-interface applications. (n.d.). https://doi.org/10.1007/s42114-026-02120-y

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02120-y

Keywords: hexagonal boron nitride, PDMS, porous membrane, thermal management, breathability, wearable electronics, skin-interface materials, perfluorohexane porogen, thermal conductivity, skin hydration, mechanical compliance, computational fluid dynamics