Clean dust-free hay or straw can also be used. Many people like these for litter as well, although in my experience they don't control odor well. Many people like to use rags, cloth diapers, or towels for bedding, but threads can sometimes get wrapped around a rat's leg or neck. I definitely don't recommend using fabric or yarn for a maternity nest or for babies. A safe and very warm alternative is felt, which is made from very short fibers.
Most rats have clean bathroom habits and never soil their bed.
Others, especially some males, aren't so fussy. When you clean the cage, check to make sure the bedding is still clean and replace it when necessary. The Cleaning Schedule Changing your rats' litter when it's soiled is vital. Bacteria starts to work immediately on urine, changing it to ammonia, which causes the strong unpleasant odor that comes from a dirty cage. Ammonia is very irritating to delicate tissues, and prolonged exposure can damage the respiratory tract.