A thermal insulation panel exhibits little or no warping due to temperature differences between different portions of the panel. The panel comprises insulation material and an envelope for encapsulating the insulation material. The envelope comprises a base member and a cover member. The cover member is supported by the base member in a floating and sealing engagement with the base member. The cover member can slide relative to the base member to compensate for differential thermal expansion effects on the respective base member and cover member. In an alternative embodiment the cover member is adapted to be exposed to a temperature significantly below the temperature to which the base member is exposed. The cover member is formed of a metal having a low coefficient of thermal expansion to compensate for differential thermal expansion effects in the respective base member and cover member. The cover member and the base member are joined to provide the envelope with a hermetic seal.