The wheel has sisal on the inside and out but even though the cushioned pads can be taken out, the carpet can’t. The wheel has a 20-inch diameter, so is absolutely only ideal for small cats and kittens, and it will maintain a optimum cat fat of 15 lbs. https://airspot-gymnastics37900.bloguerosa.com/26440838/5-essential-elements-for-cat-treadmill-wheel