The cover is a chloroprene rubber with a nylon surface, similar to wet suit material. Inside is open cell foam and a polyurethane solid GEL. When the product is described as ‘Dimensional Gel’ this is a Silicone Polymer based Gel. It is referred to as a ‘SOLID GEL’ and will not leak out.  If the cover is punctured, it may feel a little sticky.  To remove the stickiness, just coat the gel with a little baby powder.