An envelope generally comprises a sandwich of layers comprising an outer layer, outer plastic film layers affixed to the outer layer, a ceramic fiber layer, a radiant barrier layer, and one or more plastic film layers affixed to an obverse or reverse side of the radiant barrier layer. The sandwich of layers is folded over unto itself at the bottom and sealed at the sides so as to form an envelope, and the top closure being formed by folding the top downward over the folded lower portion. In other embodiments, the sandwich of layers comprises an outer radiant barrier layer and an inner radiant barrier layer, first, second, and third plastic film layers, and a ceramic fiber layer. In some embodiments, the envelope comprises a mesh layer.