Outlast Thermal Regulatory Underwear.

It works to keep the wearer’s temperature not too hot... not too cold... but just right, over a broad range of environments and activity levels.
When your activity level or the outside temperature increase, the OUTLAST thermocules that contain the phase change paraffin begin to change from a solid to a liquid which provides you with a comfortable sensation of thermal equilibrium. The energy required to activate this process comes from your warm body or the rising ambient temperature.
When you begin to cool down, OUTLAST thermocules begin to change back from a liquid o a solid. In this phase change, the energy that was absorbed by the thermocules while you were active is returned to you.