a crylon ™ gel containing glass beads and a light metal , formulated to be pliable when frozen , yet reusable and stable enough to permit repeated thawing and freezing , is contained within a vinyl package having a covering which is both hypoallergenic and waterproof . the packages are comfortably held in place , e . g . pressed against an injured portion of the body , by appropriate straps and / or fasteners , which may form a part of the package .