Hatchlings we use bounty select a size paper towels. In the adult's we use legal sized white computer paper. we have to trim about 1.5 inches off of the end but it works great
I actually use a thick fabric that is like weed fabric for gardens. Works great in the hatchling rack. I have double the amount so when I take one out to wash, the other goes in. Didn't cost that much at all.
I only use a 6qt rack system for fattie and coleonyx hatchlings and as overflow for leopard geckos, so it's not a permanent housing option with me. I don't use any substrate. They make enough mess without having to deal with shredded paper towel.
I use shelf liner from walmart because i got tired of wasting so much paper towel. i clean and reuse the shelf liner and so far it has worked very well. its pretty cheap too.