An initiator assembly for placement in an associated opening in an initiator-containing device includes an initiator device having at least one igniter element and an elastomeric overmoulding. The initiator device includes at least one of a thermoplastic initiator base and a thermoplastic adapter integrally joined to a base of the initiator-containing device. The elastomeric overmoulding is integral with at least one structural component such as the initiator base, the adapter and the base of the initiator-containing device. The elastomeric overmoulding serves to sealingly mate the initiator assembly in an initiator-accepting opening in the initiator-containing device. Also provided are corresponding methods of making an initiator assembly.