Glazing is a transparent part of a wall structure and is usually made of glass or plastic, also known as the glass part of a window. The glazing is mounted with glazing putty and a support frame that holds the glass in place. Common types of glazing include single-pane, double-pane, triple-pane, and low-emissivity and heat mirror glass. Previously, all windows were single glazed with one pane of glass. Single-pane glazing provides little protection against heat or cold. Because of the advancements made in glazing, single-pane windows are typically only used for their decorative look. Modern energy-efficient windows now come with glazing systems, which incorporate glass panes, gas fillings, and heat-sensitive coatings. These glazes include double-pane glazing, which are also referred to as insulated glass. Double-pane glazing contains a layer of inert gas, typically argon or krypton, sealed between the inner and outer glazing. Because the gas is a poor thermal conductor, it slows the flow of heat through the glazing and eliminates the need for storm windows. Triple-glazed windows are even more efficient than double-paned, as they include an extra layer of gas within the frame. In addition to providing improved thermal protection, triple-glazing can also provide sound-reduction qualities. Low-emissivity (low-E) and heat mirror glass is another option when choosing glazing. This type of window glazing includes a low-E coating and an invisible layer of metallic oxide, which reduces the amount of heat passing through the glass. Depending on locating, low-E glazing may be adjusted to allow the sun’s energy in, or to block it out. Low-E glazing has been estimated to reduce energy costs by about 25% compared to single-pane glazing. Most new windows today offer low-E glazing. Additionally, heat mirror glazing systems typically meet or exceed the energy efficiency provided by triple-paned windows without the additional weight. Heat mirror glazing is made by suspending a sheet of low-E film between the insulated glass panes. Superglass, a material known as being one of the best insulators on the market, suspends two layers of heat mirror between the glass panes with gas-filled spacers. When considering window and glazing options, it is important to consider building type, climate, utility rates, heat gains and losses, visual requirements, shading and sun control, thermal comfort, ultraviolet exposure control, condensation control, acoustic control, color effects, daylighting, and energy requirements. Other considerations may also be necessary when choosing the correct glazing.