The 20/20 episode mentioned the Tummo meditation and that he may be consciously raising his body temperature. Like giving himself a fever of sorts? One part of the show they showed footage of a test with a british special forces guy immersed in freezing water (not as cold as was used for Wim Hof's test) and he could barely stand it, literally screaming underwater. Then comes the Wim guy talking calmly, no teeth chatter, nothing. Unreal.