A hydrogen peroxide-powered engine is based on the decomposition reaction of hydrogen peroxide. Nearly pure (90% in the Bell Rocket Belt) hydrogen peroxide is used. Pure hydrogen peroxide is relatively stable, but in contact with a catalyst (for example, silver) it decomposes into a mixture of superheated steam and oxygen in less than 1/10 millisecond, increasing in volume 5,000 times: 2 H2O2 → 2 H2O + O2. The reaction is exothermic, i.e., accompanied by the liberation of much heat (about ), forming in this case a steam-gas mixture at . This hot gas is used exclusively as the reaction mass and is fed directly to one or more jet nozzles.