These massage ball are made of stone needle, which help improve body microcirculation and promote blood circulation. Therefore, these healing balls help improve your health. In addition, they help relieve muscle sore and pain. After you play these balls for a while, you will feel relaxed and the fatigue has been removed from your body. Features - Color: Black. - Material: Stone needle. - Size: 5 x 5 x 5cm (LxWxH). - These balls acn help reduce stress and anxiety, promote relaxation, improve mobility, recovery, ease pain and muscle tension. Use to reap the health of a hot stone massage like you get from professionals at home. Warm in hot tap water for minutes, dry, and begin feeling your muscles relax when you apply the soothing warmth. Heat increases circulation helping to relieve cramps and muscle spasms in all areas of the body. - These Massage Roller Balls can be used to provide either hot or cold relief as needed. Freeze a ball one day, and heat it the next. However, while you can use the balls for both hot and cold massage, you may want to buy a set of two, so you can alternate heat and cold in the same massage therapy session. Alternating hot and cold therapies with a muscle roller ball can be a great way to release tight knots into relaxed muscles after your workout and exercises.