YONEX Heat Capsule Jacket, Size L For sale. This jacket is lightweight and warm. The following is an excerpt from the manufacturer's website: HEAT CAPSULE Warmth from infrared rays This charging heat system converts sunlight and infrared rays emitted from the human body into heat, trapping the heat within the fibers. When continuously irradiated with infrared rays for a certain period of time, the surface temperature differs by approximately 3 to 7°C compared to conventional cold-weather materials. In a comparative test using a 500W reflector lamp from a distance of 1m with a temperature setting of 20 degrees, the temperature inside the Heat Capsule side clothing increased after only 60 seconds, demonstrating excellent warmth.