I don't keep rats, but I do have two male mice kept in separate big open bins in the shed. They will be breeders, if I ever find a female. I had them on CareFresh but didn't like it. I threw that out a few days ago, and put in a couple inches of yard soil from our irrigation ditches, and added a bunch of dried grass. They have big sheets of bark to hide under. They seem to be doing fine so far with that.