An enclosure of an active implantable device comprises a composite material which comprises a first layer of a polyetheretherketone film, a second layer of polyetheretherketone film (8) and, sandwiched between, a third layer comprising titanium. The arrangement may be provided in various embodiments such as comprising housing halves (70,72) and a lid (74), each being made of the three layers described. In one embodiment, a communications window may be provided which has a thinner layer of titanium, to facilitate communications between the outside and electrical components positioned within the enclosure.
