You will also want to look for a Low-E product that achieves the best color neutrality. Argon or Krypton Gas. Argon and Krypton gas are two gases that can be injected in an insulating glass unit to improve the energy efficiency of the window unit. Please note that this option is not ideal in high altitude locations. 3.Warm Edge Spacers.
Heat loss can also occur at the spacer within the insulating unit.
New warm edge technology performs better than the traditional aluminum spacers. The shading coefficient of the glass determines how much solar heat will pass through the window and into the house. Shading coefficients can range from 0.0 for an opaque unit that lets no solar radiation pass, up to 1.0 for clear, single pane glass. So the smaller the number the more effective the window is at keeping solar heat from passing through the house. This is important to note if you live in a warm climate for most of the year.