The properties of glass can be altered dramatically to suit very different tasks. Safety glasses that prevent panes from shattering into dangerous shards are physically reinforced with wire mesh for fire retardation, or with interlayered polyvinyl butyral for impact, sound, and UV ray absorption. Tempered glass is a heat-treated safety glass used in structurally demanding jobs that call for extra strength. Flat, distortion-free float glasses are used in applications where safety glass isn’t required, such as in picture frames and greenhouse glazes. Leaded glass is preferred in decorative roles, and can take on many different shapes and colours.