Isolate problem areas and release muscle tension with this 2-piece Hot & Cold Therapy Massage Balls Set featuring small balls made of durable plastic. One ball has a smooth surface for regular massaging and one has a bumpy surface for deep massaging. Simply place them in the microwave or refrigerator for hot or cold use. Balls stay hot or cold up to 20 minutes. Balls measure approximately 2.5" in diameter. Comes packaged in a hanging box. Box measures approximately 6" x 1.875" x 9.375".