The Relief Pak re-usable cold pack offers an effective method of applying cold therapy to a localized area. Place pack in a chilling unit or freezer. Packs remain pliable and soft even below freezing. Pack maintains its therapeutic temperature level for up to thirty minutes. Institutional grade packs are made of durable heavy-duty vinyl exterior and bentonite clay interior. Chilled pack should be wrapped in towel before applying to treatment area. clayinterior.Chilledpackshouldbewrappedintowelbeforeapplyingtotreatmentarea.