Lightweight materials with favorable mechanical, electromagnetic interference (EMI) shielding and thermal insulation performance are highly desirable for applications in harsh environments. Polyacrylonitrile (PAN)-derived carbon nanofibers/ carbon foams containing hollow closed microspheres have been developed, and their balanced multifunction is noteworthy. The addition of CNFs resulted in a gradual enhancement of the specific compressive strength of carbon foams, reaching a maximum value of 26.6 MPa·cm3·g−1 with content of 3 wt.% CNFs, improved by as much as 62%, compared to that of pristine carbon foam. Additionally, the fracture toughness exhibited the maximum fracture energy absorption of 118.6 MJ‧m−3 at 3 wt.% CNFs. The appropriate amount of CNFs and hollow carbon microspheres resulted in effective toughening and strengthening of carbon foams. Incorporation of CNFs into carbon foams also resulted in an improvement in their electromagnetic shielding performance, with a maximum EMI-shielding effectiveness of 65.8 dB. Reflection loss was the main contributor to electromagnetic shielding efficiency. Furthermore, carbon foams presented remarkable high-temperature thermal insulation, with a minimum thermal conductivity of merely 0.509 W·m−1·K−1 at 800 °C. They exhibited the ability to withstand the butane flame ablation at 1000 °C, which substantiated the potential of carbon foams for aerospace applications.

Carbon foam composites containing hollow microspheres, reinforced by carbon nanotubes (CNTs) and montmorillonite (MMT), have been developed as the thermal insulation and EMI shielding layer. The effects of additive amounts of CNTs/ MMT on microstructure and properties of the carbon foam composites were investigated. Results showed that carbon foam composites had hierarchical porous structure, with CNTs and MMT being relatively uniformly dispersed in the composites. The addition of multiscale additives improved the mechanical, electromagnetic shielding effectiveness and thermal insulation properties of carbon foam composites. The composites containing 0.2 wt.% CNTs and 5 wt.% MMT, showed outstanding compressive strength, up to 8.54 MPa, increased by 116% to pure carbon foam. Their electromagnetic shielding effectiveness was as high as 65 dB, increased by 75%. Due to the hierarchical porous structure and MMT’s heat barrier effect, carbon foam composites presented remarkable thermal insulation properties. The minimum thermal conductivity was 0.45 W·m−1·K−1 at 800 °C. Their exceptional thermal protection can also be evidenced by ablation resistance under flame at 1000 °C. Therefore, such multifunctional carbon-based composites are ideal for use in thermal protection.