A final aspect of our hBN polyHIPE synthesis was the difference between oil phase and aqueous phase initiation. BPO (benzyl peroxide) was utilized as an oil-soluble initiator, and KPS (potassium persulfate) as a water-soluble initiator. The results are shown in Fig. (A), polyHIPE polymerized using KPS in the dispersed water phase, and Fig. (B), polyHIPE polymerized using BPO in the continuous oil (monomer) phase. In both samples, the initiator was added before emulsification. The BPO sample polymerized quickly, taking less than 48 hours. The KPS, in the water phase, took over a week. As a result, there was ample time for sphere settling to occur, and a polyHIPE with a very brittle lower portion was obtained. This lower portion broke apart with a gentle touch, but the top half of the composite was tough, indicating a greater fraction of PS. However, burning an hBN polyHIPE in the same manner gave dramatically different results. These are shown by screenshots in Fig. . Not only did the material not drip, but it self-extinguished and glowed red rather than reigniting. The supporting information shows the full video (Fig. ). After the residual surface polymer burned, the exfoliated hBN prevented further combustion of the PS matrix. Attempts to reignite the composite would cause the composite to turn red hot where the flame was applied (Fig. ). These qualitative results were investigated further using a microscale combustion calorimeter.