A diaphragm for a lung demand valve, including a CBRN layer which is sufficiently resistant to the permeation of at least some CBRN agents and a resilient layer which is resiliently deformable. The CBRN layer is arranged to restrict the permeation of at least some CBRN agents through the diaphragm, and the resilient layer is arranged to allow the diaphragm to be resiliently deformed.
