An inflator (10) is actuatable to provide inflation fluid for inflating an inflatable vehicle occupant protection device. The inflator (10) includes a volume of stored gas and a propellant (52) that is ignitable to undergo a reaction that produces reaction products. The reaction products include heat and gas that mix with the stored gas to produce a mixture of inflation fluid. The inflator (10) is configured to discharge the inflation fluid to inflate the protection device. The propellant (52) comprises an open cell foam fuel propellant (140). The reaction includes a combustion reaction in which the foam fuel propellant (140) reacts with a gas oxidizer comprising oxygen to produce heat and gas reaction products that mix with the stored gas.