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 36 in length 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 1 Each / Each