What kind of material would I need to make molds for a microwave kiln?

I’m not sure how to word this for Google. I keep getting tutorials for the giant kilns.

I just bought a tiny microwave kiln to make fused glass pieces, and I’d like to make some molds for it. Similar to the silicone molds you’d buy for epoxy resin. What kind of material would I need? I know it needs to be ceramic, but is there a special type of molding clay for this purpose?