Hollow core and sturdy EVA foam construction. Uses less foam than an ordinary foam roller and lasts longer, too; won't break down with day-to-day use! Durable and travel-friendly, the GRID roller is also environmentally conscious. The GRID is low and flat, making it feel like a forearm, and has bumps that are high and firm, feeling like the fingertips. Great for massage. 13" Multi-Density Massage Roller for Deep Tissue & Muscle Recovery - Relieves Tight, Sore Muscles & Kinks, Improves Mobility & Circulation - Targets Key Body Parts THREE-DIMENSIONAL SURFACE - allows tissue to aerate while you roll, promoting the flow of blood and oxygen; the nutrients needed to repair muscles MEASURES - 13" x 5.5" with a 500-point weight limit INCLUDES - access to Free online instructional video library on foam rolling education from the experts at TriggerPoint