Ceramic tiles have a "multiple hit capability" problem in that they cannot sustain successive impacts without quickly losing much of their protective value. To minimise the effects of this the tiles are made as small as possible, but the matrix elements have a minimal practical thickness of about one inch (25 mm), and the ratio of coverage provided by tiles would become unfavourable, placing a practical limit at a diameter of about four inches (ten centimetres). The small hexagonal or square ceramic tiles are encased within the matrix either by isostatically pressing them into the heated matrix, or by gluing them with an epoxy resin. Since the early nineties it has been known that holding the tiles under constant compression by their matrix greatly improves their resistance to kinetic penetrators, which is difficult to achieve when using glues.