A knitted interface comprises a knitted structure formed from a plurality of elastomeric polymer filaments (6, 7) having a plurality of interstices (12) permitting a transfer of air therethrough. The elastomeric polymer filaments may have a solid or hollow cross-section. The interstices (12) vary in shape and size according to a knit density of the knitted structure upon movement or radial distension of the knitted interface. The elastomeric polymer filaments may be made from silicone.
