Reflective glass is glass that has been treated with a metallic coating to allow it to reflect heat. It is not reflective in the sense that it acts as a mirror, although some products do indeed have a highly reflective surface, but rather in the sense that it reflects radiation rather than absorbing it. This type of glass is used in environmentally friendly construction with the goal of reducing heat gain and loss, making structures much cheaper to heat and cool over the course of the year. A classic use of this type of glass is in building facades. Glassed-in buildings wax and wane in popularity around the world, and when they are in vogue, using reflective options can cut down on operating costs over the building's lifetime, in addition to making the interior more pleasant to work in. Reflective auto glass is also available for installation in environmentally friendly vehicles.