Stretch material called "Tenjiku (knit material often used for cloth-like T-shirts.)" and comfortable to wear. There are 18 1300 gauss-ferrite permanent magnets that have unique alternating arrays around pressure points in the shoulders and back. This helps stimulate blood circulation, and can have an onset of action within a couple of hours. Just wearing a tank top helps naturally dull stiffness in the shoulders, pains in the back and tired muscles after playing sports. This also helps ease tension in the shoulders whenever using a computer. This product is greatly appreciated by many customers, who said, "This is the most effective healing product for stiffness in the shoulders." In addition, you will have great fun playing golf if you wear this tank top under your shirt.