A self-contained thermal insulation panel, of generally flat rectangular form suitable for placement within the walls or doors of a refrigeration cabinet, consists of a hermetically sealed envelope surrounding an assembled framework defining a plurality of thin parallel internal cavities. The cavities are formed by a plurality of thin stretched-out sheets, each preferably with at least one reflective face, spaced-apart by thin interlocking peripheral gaskets between a top and a bottom frame member. A method of manufacturing an insulation panel according to this invention requries the initial assembly, on a first frame member, of an alternating array of thin sheets and gaskets, then a final sheet and a second frame member all brought firmly together and permanently affixed as a unified assembly. The assembled structure is then evacuated and refilled with a heavier-than-air gas of low thermal conductivity, e.g., a halogenated methane or ethane, and sealed into an outer envelope closely surrounding the frame structure which thereby defines the panel shape. In another embodiment of the insulation panel, gas-filled foam around the edges of the thin strectched-out sheets replaces the well-defined framework to form the plurality of gas-filled cavities therebetween. In yet another embodiment, gas-filled bubbles formed on one side of each sheet space it from the adjacent sheet, without a framework or foam, to generate the cavities.