What is an infrared heat cabin?

KLAFS FAQ for well-being 

The terminology: Infrared heat cabins (the official term used by the RAL Association) are often simply called “infrared cabins”. Sometimes they are also referred to as infrared saunas. In an infrared heat cabin, your body primarily absorbs the heat generated by an IR radiator or similar component, such as IR foil which heats the walls. Generally speaking, the temperature inside an infrared heat cabin is 40-45°C.