Some rat owners use fleece with litter boxes, while others use substrates such as paper or aspen wood shavings. While it's a matter of preference, they each have their downsides: fleece doesn't absorb urine well, paper bedding clumps when wet, and aspen is light and messy. Because of this, I set out to find an alternative option that is both safe and absorbent.
I normally use fleece along with 2 litter boxes in the cage, but fleece begins to stink after a few days. I find myself cleaning the cage twice a week to avoid the stench of ammonia from irritating my rattie's lungs and my nose!