The Vertx 37.5 Combat Shirt (VTX8525) features innovative dual fabric technology that is soft, breathable, and form fitting. Exclusive 37.5 Active Particle Technology fabric treatment built into the torso provides enhanced comfort under armor, plate carriers, and vests by capturing and releasing moisture vapor and keeping the body in its ideal microclimate – relative humidity of 37.5% core temperature of 37.5 degrees Celsius. Available in Black, OD Green, Desert Tan, and Smoke Grey.