A thermal insulation/breather/venting membrane (1) for use in building construction (14, 26) comprising a sheet (2) of reflective material having an outer surface (3) and an inner surface (4); a coating (5) applied to the outer surface (3) of the reflective material (2) to prevent, or restrict, oxidation; and a multi-layer sheet (6) of material including an inner, planar layer (7) bonded to the inner surface (4) of the reflective material (3); whrein the outer layer (8) of the sheet (2) of material is deformed to define a plurality of embossed, elongated air pockets, or elongated air channels (9), or is foamed.