In order to provide the proper insulation the layers of glazing must be appropriately separated by spacers. In the 1960s, window manufactures began using aluminum spacers. They soon realized because aluminum is an excellent heat conductor when used as a spacer for most edge systems there was a major heat loss at the edge of the (IGU) insulated glass unite, reducing the energy efficiency benefits. This heat loss at the edge of the IGU made the windows susceptible to condensation.

In order to correct this problem, manufacturers were forced to research and develop new edging systems. Some of these new developments included drastic designs like changing the shape of the cross-sections. Other developments were replacing the materials not uses before for windows, such as replacing the aluminum spacers with stainless steel, vinyl, or fiberglass. Window manufacturers still employ these changes today.

With the research done to improve windows, it also alerted the window corporations they also needed to create better materials for insulation. The more widely used insulation incorporates spacers, sealers, and desiccants in a thermoplastic composite containing a mixture of the desiccant material, combined with a thin, flexed, metal layer of aluminum or stainless steel sheeting. A different advancement was to use silicone foam spacer as insulation. This was done by incorporating desiccants and
strong adhesives to bond to the edges of the glass. The foam was then backed with a second sealant.

Numerous hybrid designs came out of the sudden window research. The drive to create new and improved windows designs, which incorporated such things as thermal breaks along with metal spacers or any of the improvements listed above. Some of the developments that came about were for use with multi-layered glazings or for IGUs that used stretched
plastic coatings. All of the new designs were created to interrupt heat transfer, thus improving the energy efficiency of the product.

As widow manufactures change from standard double-glazing to high-performance, warm edge spacers have become important. The U-factor is a representation of the heat flow per hour (BTUs per hour) through a square foot of window for 1oF temperature deference in the indoor and outdoor air temperature. By switching from aluminum to a less heat conductive edging, you will reduce the overall window U-factor by approximately .02 Btu/hr-sq ft-°F. Remember, the smaller the U-Factor, the lower the transfer of heat.

A better improvement would be to increase the temperature of the interior surface where condensation forms. When the temperature outside is 0°F improved thermally spacers may increase the temperature by 6-8°F (3-4°C) at the line of sight on the window or 4-6°F (2-4°C) one inch away. This is a significant development. With each new development with insulated multiple layer windows, the improvement of the edge spacer becomes more important.