Abstract: A heat insulating structure for low-temperature or cryogenic pipings, comprising at least one heat insulating barrier and at least one moisture barrier which are laid on the outer surface of a piping to be heat-insulated, and at least one sheating layer, wherein said heat insulating barrier comprises an extruded styrenic resin foam and wherein, as expressed in terms of the three-dimensional coordinates X (circumferential direction), Y (thicknesswise direction) and Z (longitudinal direction), said heat insulating barrier has a Y-axial water vapor permeability Py of 1.5 g/m.sup.2 .multidot.hr or less and at least the heat insulating barrier most adjacent to said piping has X-axial and Z-axial elongations at rupture Ex and Ez in the range of 8 to 40 percent.

Abstract: Flexibilized, rigid plastic foam sheets with improved properties particularly desirable for low temperature and cryogenic insulation can be prepared by mechanical compression of freshly expanded closed-cell thermoplastic foams. Thus an extruded foam sheet having a density of 20-100 kg/m.sup.3, a y-axial size size of 0.05 to 1.00 mm and a Y-axial compressive strength of at least 1.8 kg/cm.sup.2 is flexibilized with 0.25 to 240 hours of expansion to give a flexibilized foam with improved elongation, workability, crack resistance and water vapor barrier properties.