Squeezing out the energy : Macroscopically reversible deformation of polymers in contact with water produces H2O2 in quantities that are sufficient to drive small‐scale chemical syntheses. The amount of mechanosynthesized H2O2 scales with the polymer–water interfacial area, and the efficiency of the mechanical‐to‐chemical energy transduction can be as high as 30 % for soft, porous polymer “sponges”.