The need to restrict sound arriving from the external environment means that glass should be able to shield and insulate the internal spaces of a building. Glass type is the major factor influencing the passage of sound. The most common types of glass used are laminated and insulating glass (Double glazed). Laminated glass incorporates a special acoustic PVB interlayer, which absorbs some of the incident sound energy, reducing its passage. Better sound insulation can also be achieved with double-glazed glass in which vacuum-sealed inner spaces and some gases affect sound insulation and provide acoustic stability.