Quanex has announced the celebration of 35 years of Warm Edge Excellence this year! Wow—it seems like only yesterday. For me, it all began at a company called Tremco, well known for roofing, waterproofing and construction sealant technology. When I joined the company in 1986, Tremco was trying to break in to the fenestration market with sealants and a new invention based on an all-in-one flexible spacer system.

This flexible spacer system wasn’t invented with warm edge properties in mind—that would come later. However, the main advantage of the flexible spacer system, or Dura Platform Spacer, as it later became  known, was that it replaced metal spacer, sealant and desiccant with an all-in product thereby reducing the number of fabrication steps from 5 to 1. Dura Platform spacer also made the process of fabricating shapes so much easier and that was oftentimes our foot in the door. Bending aluminum bar was frustrating.

But in order to convince more fabricators to give Dura Platform a try, we needed another angle. One that was more marketing oriented. We were working with scientists at the University of Waterloo’s Advanced Glazing Systems Lab to analyze heat flow across insulating glass units comprised entirely of various edge seals. In other words, we built IGUs with no air gap between the glass panes—only spacer and sealant was employed. We found that this was a valid way of measuring the heat flow that was occurring at the edge of an IGU and we were able to compare Dura Platform against conventional aluminum bar spacer systems as well as silicone foam and fiberglass. What we found was that, the less metal comprising the spacer-sealant system, the less transfer of heat occurred through the edge of an IG unit. Heat travels from where it’s hot to where it’s not so cutting down on heat transfer through the edge of the IGU provided a warmer edge and less heat loss through the window.

I will never forget that first talk I gave on the subject, titled, “Warm Edge Seal Technology” at the SIGMA summer meeting on August 20, 1990 in Reno, Nev. At the cocktail party that followed, it seemed everyone was talking about “warm edge.” At the time, California was considering legislation that would establish a minimum level of energy performance for windows. Rumors abounded that this requirement was likely to involve a U-value of .65 or lower—imagine that! Now, fast forward to 2016 and Energy Star Version 6 where the Northern Zone requirement will soon be 0.27.

It was also announced around the time of this presentation that a Federal law was recently passed, known as the Sen. Wirth Bill mandating that the fenestration industry would be tasked with developing “a fair and credible means of rating and labeling fenestration products … or one would be designed for us.” It was suggested that the criterion would most likely be based upon the “Overall Window U Value” that was recently described in the 1989 ASHRAE Book of Fundamentals and that this overall U-value must now take into account corrections based upon the edge of glass area as well as the frame area. This was a huge development at the time, since prior to this, U-values had been based solely on center of glass measurements. When reported as center of glass values, an aluminum framed window with an aluminum spacer could be reported to have the same U-value as a wood or vinyl window with a non-metal spacer system. Both ASHRAE and Sen. Wirth obviously realized that this method was misleading to consumers.

After my initial talk on the subject, there were numerous road trips to speak or visit customers to discuss this so called “warm edge” concept. I remember days on the road became more numerous and time spent in the office was a rarity. I will never forget my boss at the time, often complaining, that “Jim is never here when I need him in a meeting! He is too busy running around the country warm edging here and warm edging there!”

The Window Division business unit of Tremco later became Truseal Technologies, and Duralite was added as the premier Dura Platform spacer system, touting even better warm edge performance. Super Spacer was developed by Edgetech as a structural form of warm edge. Super Spacer quickly grabbed a very respectable share of the market as a dual-seal version of warm edge, enabling outstanding durability and superior condensation resistance. Today, all of these technologies and the majority of the brilliant people responsible for their development reside under the Quanex umbrella.

Meanwhile, also in response to the warm edge craze, Intercept, developed by PPG and fueled with high capacity production systems introduced by GED, quickly grabbed a very large share of the market. Cardinal IG, with its stainless steel spacer and dual-seal design also grabbed a fair portion of the warm edge market with their XL Edge offering, and other warm edge designs soon came along as well. The conventional aluminum box spacer, once a mainstay in the residential market, soon became the minority!

So what is the next frontier for warm edge technology? Well stay tuned because opportunities in the commercial market are wide open!


  1. So, Jim, are you saying that you coined the term “warm edge”? I recently asked Jeff Baker, our industry’s “consultant to everyone” what the technical definition of “warm edge” actually was. His answer… “Not aluminum!”

  2. Actually Phil, the very first insulating glass unit patented in 1865 by Thomas Stetson could be considered ‘Warm Edge.” It was comprised of cellular wood strips or rope, and thatch or tar. So, perhaps they were talking about Warm Edge in 1865, well before our time! If the technical defintion were to be based simply on the basis of being “Not Aluminum” maybe we should have called it “NOALUM Technology.”

    In the paper that was presented, Warm Edge was simply defined as an edge seal system with high thermal resistance or “HI-TR” properties as evaluated using the test method developed at the University of Waterloo. I still have a copy of the paper and can send it to you. Their test mehod was quite interesting.

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