Molded composite 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 for ankle stretching and knee rehabilitation. Diameter refers to the width of the half-round profile. The molded rollers are strong enough to be used by large adults and active children. Foam rollers are available in 36", 18" and 12" lengths with either a round (circular) or half-round (semi-circular) profile. This line of rollers is available in black. The molded composite foam rollers are more firm than the polyethylene roller and are rugged. Black Composite - Extra Firm - 6" x 36" - Half-Round.