Constructed of a durable, burst-resistant material featuring a ribbed non slip surface. Easily used in workouts by users of all ages and sizes. Available in 4 popular sizes. Tested to support 1210 lbs. of dynamic weight. 4′ 7″ to 5′ 0″ to use 45 cm ball. 5′ 1″ to 5′ 6″ to use 55 cm ball. 5′ 7″ to 6′ 1″ to use 65 cm ball. 6′ 2″ to 6′ 8″ to use 75 cm ball. 6′ 9″ and above use 85 cm ball.