This size measures 3" x 5". It is great to take along for anything from walking the dog to overnight winter camping. It is small easy to carry and you can boil it back to be ready for use again in ten minutes. When your hands start getting cold, take out the "Handwarmer" and press the button inside the pack. In seconds the salt crystals will heat up to 130° F. By comparison most single use handwarmers warm up to about 104ºF. So with the Quantum Heat Pack, you get considerably more heat and it only takes a few seconds. It is fairly simple chemistry - the aluminum button inside triggers a reaction with the super-saturated salt and water and the salt (sodium acetate) start to crystallize. As it does it gives off heat. It is considered a moist heat and because the heat pack gets so warm, it is very effective for pain.
