This work aims to predict the thermal conductivity of microcellular and nanocellular thermal insulation foams to explore the correlation between the cellular structure and the thermal insulating properties.

An ideal dielectric material for microelectronic devices requires a combination of high anisotropic thermal conductivity and low dielectric constant (ɛ′) and loss (tan δ). Polymer composites of boron nitride nanotubes (BNNTs), which offer excellent thermal and dielectric properties, show promise for developing these dielectric polymer composites. Herein, a simple method for fabricating polymer/BNNT composites with high directional thermal conductivity and excellent dielectric properties is presented. The nanocomposites with directionally aligned BNNTs are fabricated through melt‐compounding and in situ fibrillation, followed by sintering the fibrous nanocomposites. The fabricated nanocomposites show a significant enhancement in thermal properties, with an in‐plane thermal conductivity (K_‖) of 1.8 Wm⁻¹K⁻¹—a 450% increase—yielding a high anisotropy ratio (K_‖/K_⊥) of 36, a 1700% improvement over isotropic samples containing only 7.2 vol% BNNT. These samples exhibit a 120% faster in‐plane heat dissipation compared to the through‐plane within 2 s. Additionally, they display low ɛ′ of ≈3.2 and extremely low tan δ of ≈0.014 at 1 kHz. These results indicate that this method provides a new avenue for designing and creating polymer composites with enhanced directional heat dissipation properties along with high K_‖, suitable for thermal management applications in electronic packaging, thermal interface materials, and passive cooling systems.

POSS@PVTMS aerogels with bimodal nano-sized cavities for highly efficient passive cooling (ΔT = 3.7 °C) and high-frequency THz communication (average transmission rate 88.7%).