The chattanooga hydrocollator moist heat hotpac is a therapeutic heat pack designed for providing moist heat therapy. it is typically used in physical therapy settings, rehabilitation centers, and for personal use at home. the hotpac is filled with a special clay material that retains moisture and can be heated in a hydrocollator (a water bath designed to heat moist heat packs) to deliver consistent, soothing heat to specific areas of the body.