Polystyrene (PS, (C8H8)n) is a versatile and widely-used thermoplastic polymer. Characterized by its clear, hard, and brittle nature, it can also be produced as a foam material known as expanded polystyrene (EPS) or extruded polystyrene (XPS), which is valued for its insulating and cushioning properties. PS has a relatively simple structure, which lends to its clarity when molded into products. It is also easily processed and can be molded into a wide variety of shapes and products. Due to its amorphous structure, PS has a consistent refractive index, which makes it favorable for many optical applications. Common uses of polystyrene include disposable cutlery, CD cases, and plastic model assembly kits. In optics, its properties can vary slightly depending on manufacturing processes and additives. While it is inexpensive and easily fabricated, polystyrene is not very resistant to chemicals and can be affected by sunlight over time, causing yellowing or degradation.