Kayo-wool is a spun ceramic blanket (with other ingredients) that can withstand various high temperatures. For instance I use in my forge doors, and other applications a 2.5 inch thick, 2600 degree “kao-wool”. This is sold anywhere that sells to glass blowers, pottery and ceramic dealers, blacksmiths, bladesmiths, heat treating furnaces, and kiln makers. It comes in other brand names. Durablankett is one.

Here is a great link for the US of a company selling ceramic and other hi-refractory items for making forges capable of temperatures up to 3000 °F degrees.