Design, Structure, and Material: The outer shell and base are made of high-quality, pet-safe compressed wood (MDF) or plywood. Color: Comes with a distinctive warm yellow exterior paint. Base: A wide, low wooden base, designed in an arch shape to provide maximum stability and prevent the wheel from shaking or tipping over during the cat's fast run. Inner Track (Walkway) Lining: The inner track is fully lined with durable fabric carpet (in dark gray). Function: The carpet provides excellent grip for the cat's claws to prevent slipping, protects their paw pads while running, and acts as a natural scratching post to trim their claws. Cleaning: The carpet is attached with Velcro tape, making it easy to remove for washing or vacuuming hair. Mechanism and Approximate Dimensions Silent Movement: The wheel relies on rollers or ball bearings at the back, ensuring smooth and low-noise rotation so as not to disturb the cat or cause noise in the house. Suitable Size: The inner diameter of this category of wheels typically ranges between 90 to 100 cm, which is the ideal size (L or XL) that allows adult cats (like the tabby cat in the picture) to run with their backs completely straight to protect their spine from bending.