Abstract: A hermetically sealed pouch encloses both a porous mass of material of relatively low heat conductivity and a charge of a gas having a coefficient of thermal conductivity lower than that of air and thoroughly permeating the porous mass of material. The pouch is constructed of confronting sheets of multi-ply laminate material sealed along free edge portions thereof, and comprising an inwardly facing sealing layer of 15 pounds per ream low density polyethylene, a layer of 0.5 pounds per ream vinyl primer, a layer of 0.35 mil aluminum foil, a layer of 9 pounds per ream white low density polyethylene, and an outwardly facing layer of polymeric material selected from the group consisting of polyester and oriented polypropylene.