there is a list of articles on this High End USA sauna makers site summarising most of the interesting research on the topic
https://sauna.space/pages/saunaspace-incandescent-therapythings i picked up
-NASA did a lot of the original research into the particular frequencies that had optimal cellular effects
-near infra red - seems to be where most of the research backed detox and cellular effects occur
-near infra red is from incandescent bulbs - not mats
-its the bulbs themselves that are the key to making these - they are just a Philips health lamp bulb
- the rest is window dressing / refinements
I made myself a sauna based on the sit-in one on this site - using the same bulbs but with more of them and better controls for a couple of hundred dollars