SAN is similar in use to polystyrene. Like polystyrene itself, it is optically transparent and brittle in mechanical behaviour. The copolymer has a glass transition temperature greater than 100 C owing to the acrylonitrile units in the chain, so making the material resistant to boiling water. Uses include food containers, kitchenware, computer products, packaging material, battery cases and plastic optical fibers. It is structurally related to ABS plastic, where polybutadiene is colpolymerised with SAN to give a much tougher material. The rubber chains form separate phases which are 10-20 microns in diameter. When the product is stressed, crazing from the particles helps to increase the strength of the polymer. The method of rubber toughening has been used to strengthen other polymers such as PMMA and nylon.