Hydrocollators like the Chattanooga Hydrocollator Packs - HotPac Moist Heat Packs & Steam Packs do retain heat better than most other heat packs. They can be used for hundreds of different treatments and therapies. Once they are heated through, they can disperse heat into the damaged tissue for a long period. Heat relief can be very beneficial to many muscle and joint pains and can also be used to maximize comfort and improve circulation, as well. Please note: If a hydrocollator heating unit is not available, they can be soaked in water and then microwaved.