I always use 2 inch refractory wool since it keeps its shape nice, but 1 inch would be good enough. Slap a layer or two of sealant/coating on that, and you should be good to melt anything up to 1200C.



There are some awesome electric furnace videos out there, with VOG on youtube having one of the neatest setups I've seen. I recommend playing around around with whatever you have laying around until you have something that works the way you want it, then spent the time and money to make that setup into something a little more permanent.