When low-emissivity coatings are applied to the inside surface of the glass, the radiant heat is reflected back into the building. The space in between the sheets of glass can then be filled with argon or krypton gas. These windows have either a vacuum between the panes or are filled with a transparent, non-conducting material. Frames, Dividers and Open Windows Other factors, however, also affect thermal windows. This is why it is important that frames should not be metallic.
Wood is a good insulator, as well as fibreglass, or vinyl when reinforced with wood.
For this reason, it is also a good idea to reduce the area of window frames for high-performance windows. Rather than 2 small windows, for example, it would be better to have one larger window with as few dividers as possible so that only a minimum amount of heat is lost through the frame. This should be done because, although one would naturally assume that more heat would be lost through the window, with these new heat-efficient windows, more heat is actually lost through the frame. As well, fixed windows are best since they have the smallest amount of air leakage and are generally the least expensive. Even though the R-value system had been extremely useful up to this point, it was found that it unfortunately had no way of taking into account the different factors other than that of the glass, that affected the overall thermal performance of a window.