I am not sure how large a full grown rat is. I used mine for dwarf hamsters. I think they would fit a regular size hamster. There is a larger size that might be better if your rat/family member is larger. When I use them, I took most of the bedding out & put some back in, that way my hamsters could either use it as a bed or toy/ tunnel to crawl through. I cut mine in half because dwarf's are smaller, but they last a long time if you rat is not a big chewer (some dwarfs chew a lot, my last one did not). They are great entertainment though. Check out the other size & the size of your rat & see which would be better would be my suggestion.

Yes it is. It just regular plain cardboard.

The main concern about fluffy bedding is either the hamster will ingest it accidentally or they will get their feet tangled up in the cotton ball. Though it’s really rare and just look out for it, if it happens. Hope that helps!