The Therapeutic Rock Mat stimulates over 200,000 foot nerve endings and increases proprioception. Firm foam applies pressure to specific parts of the sole of the foot and releases tension. Train natural proprioceptive capacity by standing and walking on the Rock Mat in the comfort of your own home without having to go out doors. Why was the Rock Mat XL created? The Rock Mat XL was designed to enhance our current Rock Mat by providing more space to move and train on. The larger mat can cover a greater surface area for those who have lined their home gyms, clinics, and offices with it. Density: The regular Rock Mat is a Medium-Firm, the Rock Mat XL is Firm. Fun Fact: The idea for the XL Rock Mat XL came directly from a head trainer at the LA Lakers. It's the perfect pre-game tool in their locker rooms. Dimensions: Rock Mat: 21" by 12" Rock Mat XL: 29.5" by 16.5"