The wheel has sisal on the inside and out but while the cushioned pads is usually eliminated, the carpet can’t. The wheel has a 20-inch diameter, so is de facto only well suited for tiny cats and kittens, and it will maintain a maximum cat fat of fifteen pounds. https://cruzgkjkj.blogoscience.com/32807332/a-simple-key-for-cat-exercise-wheel-treadmill-unveiled