Our Long Sleeve Shirt provides soothing warmth that’s particularly helpful for shoulder, upper back and arm discomfort. How do we accomplish this? With Back on Track’s specially designed fabric - Welltex, a blend of polyester with ceramic powder melted into the threads. Thermal l heat is a well-recognized method used for healing injured muscles, joints, and tendons. For injury prevention, you can wear this shirt prior to exercise to loosen and warm up muscles. Some people wear it in the winter for additional warmth. The Cotton/Polyester blend is a ribbed material, whereas the Polypropylene is smoother.