Searching for a fireproof sponge?
Fiberfrax is the standard material for high temperatures in refinery, chem. plants, etc. There are also other brands , all readily available on the net. Ads do not give detailed composition other than &quot;alumina and silica&quot; .  Fiberglasses may not have  high melting /softening temperatures. There are higher temperature fibers like thoria, but are expensive and not easy to find.