These hand exercisers help to strengthen the grip and increase dexterity and mobility. They are ideal for hot or cold therapy... To heat, you may place the hand exerciser in a microwave for no more than 10 seconds. To chill, you may place the hand exerciser in a freezer for up to 30 minutes. They are also easy to clean... just wash with warm soapy water and pat dry with a towel. Four color coded levels are available to meet a range of applications. Each exerciser comes with instructions.