The wheel has sisal on the inside and out but whilst the cushioned pads may be taken out, the carpet can’t. The wheel has a 20-inch diameter, so is really only well suited for little cats and kittens, and it will hold a utmost cat weight of fifteen pounds. https://myleskyfl93692.idblogmaker.com/26565498/a-review-of-wheel-treadmill-for-indoor-cats