To provide thermally insulating ware which is made of a synthetic resin and maintains thermally insulating performance for a long period of time and a process for production which improves fabrication workability and improves the production yield of this thermally insulating ware.

A thermally insulating layer body 6 formed by sealing low-thermal conductivity gas Z into a gas sealing vessel 7 consisting of a synthetic resin having a high gas barrier property is disposed together with an adsorbent M into a gap part 5 of a vessel of a double wall structure obtd. by housing an inside vessel 3 made of the synthetic resin into an outside vessel 4 made of the synthetic resin having the shape resembling the shape thereof integrating both vessels by coupling their respective aperture ends 3a, 4a, by which the synthetic resin of the gas sealing vessel 7 is maintained at a dry state at all times. The thermally insulating vessel which holds the gas barrier properly and maintains the thermally insulating performance of the thermally insulating layer body 6 is thus obtd. At the time of production, the moisture content of the synthetic resin of the thermally insulating layer body 6 is adjusted to ≥3 wt.% to enhance the impact resistant strength of the synthetic resin. Such thermally insulating layer body is disposed together with the adsorbent M into the gap part 5 and the inside and outside vessels are integrated by coupling.