The Wim Hof Method descends from a Tibetan Buddhist practice of inner fire. Here is what tummo actually is, what Hof kept, what he changed, and which path suits which purpose.
The inner fire of Vajrayana Buddhism
Tummo (gtum-mo, "inner fire") is a Tibetan Vajrayana Buddhist practice combining forceful breathing, breath retention and detailed visualisation of heat rising through the body's central channel. Its purpose is spiritual transformation - burning through mental obscurations - with the famous physical heat as a by-product used to test mastery, traditionally by drying wet sheets on the practitioner's back in freezing air.
Tummo belongs to the Six Yogas of Naropa and is taught within a lineage, under a teacher, usually after years of foundational practice. The visualisation is not decoration: in the tradition it is the engine, and studies of Tibetan practitioners suggest the meditative component, not just the breathing, contributes to the measured temperature effects. It sits inside the same Buddhist framework as the practices in our Buddhist teachings and meditation practices guides - a path, not a protocol.
From monastery to method
Wim Hof learned breathing and cold practices partly inspired by tummo and stripped them to a secular core: the vigorous breathing rounds and retention survived; the visualisation, the lineage, the teacher and the spiritual goal did not, replaced by cold exposure and commitment as pillars. The result is easier to learn, easier to study scientifically, and aimed at resilience and wellbeing rather than awakening. Both facts can be true at once: the method is a genuine, well-documented practice in its own right, and it is not tummo - the same relationship secular mindfulness has to the Buddhist path it was extracted from.
Practically: to learn the modern method, start with the Wim Hof breathing guide and the cold exposure ramp. To meet the tradition it came from, the door is the wider practice of meditation and Buddhist study - and for tummo itself, a qualified teacher in the Tibetan tradition, not a webpage.