• A directional freezing technique using polyimide enables vertical alignment of graphene nanosheets, significantly enhancing through-plane thermal conductivity.
• The PG/PDMS composite with 21.1% PG achieves a through-plane thermal conductivity of 14.56 W·m−1·K−1, 81 times that of pure PDMS.
• The method recycles scraps of highly conductive graphene films, offering a sustainable approach for TIM fabrication.
• The polyimide-assisted alignment improves the order and density of the foam, enhancing both mechanical strength and heat transfer performance.