A gas generator includes an outer wall delimiting a first chamber, a source of gas and a second chamber for diffusing gas outwards between which is found a nozzle. The nozzle includes a first through-hole for letting through gas from the first chamber to the second chamber. The first hole is closed by a cap capable of being opened from the triggering of an electro-pyrotechnic device located towards the first chamber. The second diffusion chamber includes in the wall at least one second through-hole for letting through gas outwards. The outer wall includes at least one overmolded plastic material around a portion of the metal nozzle.