Abstract: The balloon according to the invention is formed by heat-sealing at least one heat-sealable sheet which comprises a plastic film and a metal vapor deposition layer formed on one side of the plastic film. The metal vapor deposition layer is discontinuously formed so that the sheet has a metallic but insulating surface. Resultantly, the balloon having a dielectric breakdown voltage of not less than 1000 V can be easily obtained. Preferably, the metal vapor deposition layer is formed in a state of islands in the sea, the size of the island being 200 .ANG. to 1 .mu.m and the interval between the islands being 100 .ANG. to 5000 .ANG..

Abstract: The sheet material for packaging electronic parts consists of a laminated material which comprises a transparent plastic film layer and a thin metal film layer having a light transmittance of at least 25% and an electric resistance of less than 10.sup.8 ohms/cm.sup.2. The sheet material is heat-sealable at the surface of said metal film layer. An envelope for packaging electronic parts is made of the sheet material by heat-sealing in a state of disposing the plastic film layer outside.