I just stumbled onto this industrial material surplus yard. Good thing it’s not close to me or I’d be spending a lot of cash there. This high temperature insulation looks interesting. I’m not sure what it’s rated for. Apparently they have several warehouses around the country but headquarters is in Illinois.
https://seattle.craigslist.org/see/mad/d/unused-rayon-felt-insulation-heat/7206556441.html
girl power ... turns out to be about a hundred watts. But they seriously don't like being connected to the grid. Tiny ad:
A rocket mass heater heats your home with one tenth the wood of a conventional wood stove