Organic peroxides are organic compounds containing the peroxide functional group (ROOR'). If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RC(O)OOR. The O-O bond easily breaks, producing free radicals of the form RO·. Thus, organic peroxides are useful as initiators for some types of polymerisation, such as the epoxy resins used in glass-reinforced plastics. MEKP and benzoyl peroxide are commonly used for this purpose. However, the same property also means that organic peroxides can either intentionally or unintentionally initiate explosive polymerisation in materials with unsaturated chemical bonds, and this process has been used in explosives. Organic peroxides, like their inorganic counterparts, are powerful bleaching agents.