AbstractPhotothermal materials can improve the photothermal conversion efficiency. Here, we design and prepare a photothermal material which has both high light harvesting ability and high thermal conductivity for efficient utilization of light energy. Polypyrrole (PPy) was polymerized in the surface of boron nitride (h‐BN) to form polypyrrole/boron nitride (h‐BN/PPy) composites. The h‐BN/PPy composites can be dispersed in glycol‐water solution to form nanofluids with photothermal conversion properties. To further expand the field of h‐BN/PPy systems. By loading h‐BN and PPy on melamine sponge, MF/h‐BN/PPy composite sponges (MFBP) with high hydrophobicity was creatively obtained. The composite sponges can float on the surface of simulated seawater and has rich porous structure, which is conducive to the escape of water vapor. The evaporation rate of simulated seawater reached 1.21 kg m−2 h−1. Such a composite with simple preparation process and low energy consumption but high photothermal conversion efficiency has promise in photothermal conversion.