Freezing and perspiring are strength-draining measures which the body employs to maintain a feel-good temperature of 37° C. To conserve on valuable energy, the X-Bionic® UnderGear Energy Accumulator actively supports these natural physical reflexes. By maintaining a fine, intangible film of perspiration directly on the skin, the patented 3D BionicSphere® System cools the user when he perspires and warms him before he gets too cold. Precisely dosed and targeted evaporation activity provides controlled evaporation cooling. If the user is not perspiring, then the insulating effect of the knitted fabric takes hold.