The cooling The cooling effect of X-BIONIC® Underwear is only activated once you start sweating. Its clever regulation system works with the most reliable of starters: your sweat. One of a kind, effective, always just in time with its cooling power. Regulates climate control, developed by scientists, tested by endurance athletes. You know that unpleasent feeling of having just sweated and then getting goose bumps afterward. Your body is sounding the alarm: Caution, overcooling risk. X-BIONIC ® Underwear prevents these chills. if no sweat is present, then a unique process uses air heated by the body as thermal insulation.