Abstract <p>This article describes in detail the design of a cryostat developed by the authors, which has high thermal insulation properties. The development is based on the possibility of performing phase transitions of the working fluid from a gaseous state to a liquid, and then to a solid in a hermetic cryostat jacket. The processes of phase transitions occurring in the jacket should be considered as isochoric, since they occur in a closed volume of the jacket. The increase in thermal insulation properties is ensured by the fact that the hermetic space of the jacket is filled with a working fluid in the form of a heavy monatomic gas with low heat capacity and static thermal conductivity (for example, xenon, krypton or an azeotropic mixture of gases or freons). These gases have a condensation and crystallization temperature higher than the temperature of the cryogenic liquid stored in the inner vessel (e.g., helium, hydrogen, neon, nitrogen, oxygen, argon, methane, liquefied natural gas). The cryostat design is described in detail, calculations are given to justify the rational choice of the working fluid for filling the cryostat jacket. When operating this cryostat, there is no need for vacuum pumps, as well as operating costs for maintaining a vacuum. Partial preservation of thermal insulation properties is also ensured in the event of an emergency depressurization of the jacket from the outside. In addition, the operational safety of storing explosive or toxic cryogenic liquids is increased.</p>