Collapsible heat insulating mattress having foam lattice cells and a slit foil sheet covering

A collapsible, heat insulating mattress is provided comprising at least one lattice structure of a foamed plastics material which has an open lattice structure in the relaxed condition, and metal coated foil coverings on each side of the lattice structure with slits extending across the lattice openings. When the mattress is to be stowed it is squeezed to close the lattic openings and occupy less space. The slits allow the coverings to crumple and remain undamaged when the mattress is squeezed for stowing. The coverings may be sheets with the slits cut in them, strips laid side-by-side, either abutting or overlapping, and adhesively secured only at the lattice junctions to the lattice structure.