An inch seems like a little much to me, but that's just my preference. I use about 1/2 to 3/4 of an inch I would guess. Use whatever you have to so the belly temp will be 90-94 with the bottom underneath that 95 like del said. Having the urine soak to the bottom is no problem. You'd have to use a few inches of aspen to prevent that, which really isn't necessary.