An inflator for an airbag comprises a bottle (2) containing a pressurized oxidizable gas and a bottle (4) containing a pressurized oxidizing gas, the bottles being connected with a structure (12, 16) providing a chamber (14) that has an outlet, for example provided by a conduit (16), for connection with a vehicle airbag. The bottles have respective first discharge openings (18) and further discharge openings (18a) sealed by respective sealing foils. The inflator includes a first pyrotechnic squib (22) which when fired causes the sealing foils over the first openings (18) to rupture to allow the gases from bottles (2, 4) to pass into chamber (14) and then into the airbag, and also includes a further pyrotechnic squib (22a) which is fired some time after the squib (22) and causes the sealing foils over the further openings (18a) to boost the discharge of gases from the gas bottles. In this way, and by selecting the relative sizes of the first and further discharge openings (18,18a) the inflation rate of the air bag with respect to time can be fitted to a desired profile.