Breaking the Trade‐Off Between Thermal Insulation and Electromagnetic Wave Transparency Via a Bilayer Fluorinated Aerogel With Phase‐Change Microcapsules

ABSTRACT To overcome the conflict between sustained thermal insulation and electromagnetic wave transparency under extreme conditions, this work designs a bilayer fluorinated aerogel composite. The outer layer consists of a unidirectional fluorinated polyimide (FPI) aerogel with a rigid molecular skeleton, whose porous architecture delivers low thermal conductivity (39.6 mW m −1 K −1 )), high porosity (91.9%), an ultra‐low dielectric constant (1.039), and hydrophobicity (water contact angle: 124.6°). The inner layer is a fluorination‐modified poly(vinyl alcohol) aerogel embedded with silica‐encapsulated phase‐change microcapsules as thermal buffers, offering a high latent heat capacity (153.8 J g −1 ), maintained porosity (76.7%), and a low dielectric constant (1.26) while ensuring leakage‐free thermal cycling. The combination of the two layers provides a gradient thermal protection: the outer layer suppresses steady‐state heat conduction, while the inner layer buffers transient thermal shocks through latent heat absorption. When placed on a 300°C hot plate, the bilayer composite maintains a low surface temperature of 58°C. Moreover, both layers preserve wave‐transparent performance, as confirmed by Bluetooth communication tests that achieved reliable signal transmission within 4.5 s without noticeable delay. This bilayer design offers a viable route for aerospace communication systems that demand both thermal management and electromagnetic wave transparency with high signal fidelity under harsh thermal environments.