Thera-Band Hand Exercisers are specially formulated polymer-based* exercisers available in progressive levels of resistance in five translucent colors. Two sizes (standard and extra large) accommodate most hand sizes. They're used for hand, finger and forearm strengthening, as well as hot and cold therapy. Progressive resistance in different levels of compression allow each exercise to be geared to the patient. Use the standard size hand exerciser for smaller hands. The Extra Large size was designed for arthritis victims and people with larger hands who are undergiong physical therapy or strength training. An elongated ball, it is one-third larger than the oringinal hand exerciser. Heat in a microwave for 5 second increments and test to find the ideal time for each microwave unit (all microwaves are different), usually no more than 15 seconds maximum. Cool the Hand Exerciser in a refrigerator for 1.5 to 2 hours. The softer yellow and red models fill the gap between putty and spring devices and they're not as messy as putty. *The Hand Exerciser is made of a patented non-latex polymer developed specifically to allow full range of motion of the hand and fingers with a consistent resistance throughout the exercise.