Cryogenic storage container

A container for storing materials at low temperatures comprising an inner vessel for holding such material;

• a larger outer gas-tight casing having rigid self-supporting walls around said inner vessel of such size to form an intervening evacuated load-free space at an absolute pressure less than about 0.5 micron mercury, said space containing multi-layered thermal insulation comprising thin flexible sheet radiation barriers being supported by and in alternating relation with low conductive fibrous sheet layers in the permanently pre-compacted form weighing less than 2 grams/ft.sup.2 and being comprised of fibers having 3-40 microns effective diameter and an intrinsic thermal conductivity of less than 0.2 BTU/hr-ft.sup.2 -F/ft, said fibers being arranged in overlaying crossing relationship in planes parallel to the sheet surface with at least 1% (by number) of the fibers being heat softenable and heat self-bonded directly to each other at some of the cross-points without external binder, and said fibrous sheet layers undulating within the spacing between adjacent radiation shields over a transverse distance substantially wider than its thickness, contacting first one shield than the other facing shield.