15cm diametered space provides quite large capacity. for your lovely hamster & agrave; running, no need to worry that this ball toy will squeeze your pet. Exercise running about, making it more enjoyable for the hamster more motivated to keep in good shape . fun exercise toy to maintain alertness agility, also helps & agrave; Unleash their negative emotions. Designed with multiple airflow bands, this exercise ball has high permeability. & agrave; air, not suffocate & agrave; your hamster. Big for hamster yet small for you, its portable size is convenient for you to carry & agrave; the exterior, allows you to use whenever you want to offer & agrave; your little pet an exercise. Made of high quality plastic material, this ball is durable sturdy, even if the exercise ball collides, it will not break, not easy to use. wear & agrave; corrosion.