It's actually fleece, but it's the "sheepskin" type - it costs a little more, but they seem to like it. The bottom is almost like a denim/canvas type of material. The carpets actually came with the cage we bought from Craigslist - they are custom-fit for each floor of the cage and they have hooks to keep them in place. So far, the boys haven't tried to chew it, and we've had them for about 5 weeks now!