Polystyrene is an amorphous plastic that can be clear or opaque. In its foam form, polystyrene is commonly used for foam takeout containers. In its solid form, there are different types of polystyrene: general purpose polystyrene (GPPS) and high impact polystyrene (HIPS).
GPPS is somewhat brittle and can be prone to cracking, while HIPS is made with the addition of rubber to increase its durability. GPPS is clear, while HIPS is opaque. In injection molded, polystyrene's best quality is its reliably uniform shrinkage as the plastic cools. It's a thermoplastic which means it melts when heated to a certain temperature. This makes it a viable option for injection molding.