Easily attach to standard 6" round foam rollers, allowing users to enhance their existing foam roller investment. Patent-pending design offers customization, progression and versatility. Ridged surface and 4 progressive densities support varying degrees of tissue mobilization. Yellow (X-Soft) provides extra cushion for more delicate patients through Blue (X-Firm) for advanced fascia mobilization. Include detailed color instructions featuring general techniques and advanced exercises divided by muscle region. Highly durable closed-cell foam extends product life and maintains its form.