The word `` glass '' can also refer to a drink container . It does not have to be made of glass , but can be made of any material , for example plastic . Their chemical , physical , and in particular optical properties make them suitable for applications such as flat glass , container glass , optics and optoelectronics material , laboratory equipment , thermal insulator ( glass wool ) , reinforcement materials ( glass-reinforced plastic , glass fiber reinforced concrete ) , and glass art ( art glass , studio glass ) .