Our Large 23" Sandbags are made of a grippy, water resistant material and loosely filled with silica sand. The loose sand design provides the option of low density section within the sandbag to allow for light/no pressure area on the animal (such as the chest) to prevent movement during radiographs.  The loose design is also great to use to be wrap on extremities. The covers are designed with grip in mind - removable, washable suede type covers that stick to the table and do not slide.