The concept of this vest is to have a passive cooling system based on two phase changing heat transfer features; heat pipe technology for high level heat transfer and phase changing materials for heat storage.

The benefit of such concept is to have a passive cooling system, based on known technologies, which removes heat from a human body.

The body heat is transferred by conduction to the flat heat pipe evaporator. The working fluid in the heat pipe changes from liquid to vapor (latent heat of vaporization) and flows to the condenser side. While the vapor condenses back to liquid, the heat is released to the phase changing material module in direct contact with the flat heat pipe (latent heat of condensation). When heat is applied to the phase changing material, it changes from solid to liquid phase (latent heat of fusion).

The flat heat pipes are integrated to the vest, while the phase changing material modules are situated in open pockets.
When the phase changing material modules are all liquid, they are removed and replaced by solid phase phase change material modules.

The thermal contact resistance between the flat heat pipe and its heat exchanging surfaces (body to evaporator and condenser to phase changing material) is decreased using thermal contact material (as commonly used in electronic cooling).