BycoreGlide™ charcoal firm patent-pending foam rolling and back pain exercise support device. The darker foam wears better than the white foam. Recommended for those who want deeper and firmer contacts and/or are larger people who may also be taller. People with poor balance. Whose body movement challenges require extra surface area to support themselves. This 2" height valley and wider base may work better to improve back flexibility and finally engage your abs during core exercises. You may also choose this if you want more balance support and only use this for your pelvis and hips and not the core exercises. Email our website if you have questions.