The invention relates to a housing (8) for a functional element (5), in particular for use in the medical field in naturally occurring vessels in the body, the housing wall of which has a slack, flexible, tensionable membrane (8a) with a plurality of formed parts (8b, 8c) secured thereon which support the membrane in the tensioned state thereof. Hence the housing can be expanded and compressed easily, the membrane being supported effectively in the expanded state by formed parts.