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At the core of a true success story

A few years ago, Danish window producer Krone Vinduer introduced the revolutionary COto® System; a patented window system which today is one of Krone’s most valuable inventions. A vital part of the system is a composite profile developed by Primo in close collaboration with Krone Vinduer.

The COto® System is a high-end window system with exceptionally low heat loss properties. In fact, a COto window has a documented U-value as low as 0.6 W/m2K for the combined frame and glazing, all achieved by a combination of triple-glazing and an innovatively designed frame.

A central part of the frame is a complex composite extruded profile produced by Primo. The material is extremely rigid and stable and will not degrade over time – and, last but not least, it offers superior heat retention properties compared to aluminium.

Development and close collaboration from day one

The development of the new profile took place in close collaboration between the specialists at Krone and Primo.

At first, a 3D-printed prototype of the profile was produced, discussed and corrected. Once the prototype was approved, extrusion tools were made and test runs begun at Primo’s own laboratories.

After further testing and approval, production could commence – all in all, the entire process took less than a year from the very first meetings to full production. And, of course, rigorous testing goes on during production, where shrinkage, tolerances, impact resistance and so forth are continuously measured and documented.

“Primo saw the benefits of our system right from the start,” production manager at Krone Vinduer Carsten Lanzky Jensen says, “and with their 3D printing technology, the time it took to produce the first workable prototypes was really short. That, and their knowledge and enthusiasm, made a huge difference in turning this project into a success story.”

Combining low U-values with high stability

Carsten Lanzky Jensen explains: “The challenge is to combine stability with low heat loss – most materials are simply not rigid enough when their insulation value increases. We were also looking for a composite that could last for decades, just like the rest of the window components. Finding such a material can be tricky, but with Primo’s profiles, we have a composite material that can deliver all of these benefits.”

Both the aluminium parts and the profile are produced to very fine tolerances in order to ensure a perfect fit between the aluminium cover and the underlying profile. The result is a strong and stable window frame that will look good, stay strong and keep its owners warm for decades to come.


Krone Vinduer is a leading manufacturer of low loss energy windows and doors with a strong focus on traditional wood windows of high production value. Krone also produces various series of composite windows and wood/alu-windows and doors, all rooted in the strong Scandinavian design tradition and energy efficiency.

The COto® System is used in Krone’s own production and is also sold under license to several European window production companies.

To date, close to 150,000 windows have been produced with Krone’s COto® System.


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