The present invention concerns a functional film material comprising a substrate layer and a coating layer, the coating layer comprising a block copolymeric binder and a particulate metal pigment therein, the ratio of pigment to binder in the coating layer being selected with reference to the coat weight to provide the functional film material with an emissivity of less than 0.5, and the substrate and coating layer being selected to provide the film with a VWTR (ambient) in excess 400 gm−2d−1 bar−1.