The first choice for physical therapists, physicians, chiropractors, athletic trainers and kinesiologists for nearly 60 years. Since the introduction of the Hydrocollator HotPac in 1947, thousands of doctors and therapists have insisted on this classic treatment modality. Easy-to-use: immerse in Hydrocollator Heating Unit (sold separately), remove and wrap in terry cover and toweling and apply to treatment area.