Polyethylene foam rollers are perfect for positioning, balance, postural and muscle re-education, spinal stabilization, body awareness and coordination, and ranging and strengthening activities. Round rollers offer progressive exercise sequences - user can graduate from an easier (smaller diameter) to a more difficult (larger diameter) roller. Half round roller is a great tool forankle stretching and knee rehabilitation. Diameter refers to the width of the half-round profile. The foam is strong enough to be used by large adults.