TriggerPoint GRID foam rollers feature a trademarked style that uses a superior, multi-density outside built over a stiff, hollow core that holds up against repeated use while maintaining shape and integrity. The proven toughness of the GRID has helped make it a trusted tool of physiotherapists, massage therapists, athletic trainers and expert athletes. The GRID can be utilized to roll through tight muscles, knots and kinks to decrease soreness and improve mobility. Routine use of the GRID can provide benefits such as recovery from (or avoiding) injuries, reduced muscle and joint discomfort, increased blood circulation and versatility, enhanced balance and mobility and preparing the body for peak performance. The unique, multi-dimensional surfaces of the GRID replicate the sensation of a massage therapist's hands - wide and flat like the palm, long and tubular like the fingers, and little and company like the finger tips. The textured surface area of the GRID helps to take full advantage of the circulation of blood and oxygen to heal tissue. TriggerPoint GRID foam rollers are available in three sizes and 2 densities. Routine density designs include the initial 13-inch GRID, the 26-inch GRID 2.0, and the 4-inch travel-friendly GRID Mini. The 13-inch GRID X includes extra thick foam for working the tightest muscles. Purchase of any TriggerPoint GRID foam roller consists of open door to an online training video library from the specialists at TriggerPoint that show the best foam roller techniques. 1-year service warranty.