I’m often asked: how do you choose an insulating glass unit? There really are a few important points to keep in mind. Whether it’s a window, a large panoramic storefront, or a sliding system—the right IGU is absolutely essential.
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What is an insulating glass unit?
An insulating glass unit is a construction made of several panes (at least two) separated by a cavity—the chamber—which can be filled with inert gas or dry air. The panes are hermetically joined by a perforated aluminum spacer frame and sealant (silica gel, molecular sieve, or a mix). If you choose the wrong IGU, serious problems may arise and you could end up replacing the glass. In this article I will cover 7 key points to help you make the right decision.
What’s the difference between single‑ and double‑chamber IGUs?
You’ve probably heard that IGUs can be single or double chamber. So what’s the difference, and is it worth paying more?
A double‑chamber IGU is roughly 50 % warmer than a single‑chamber one, which is why we always install them in residential buildings. They are used even for large formats—6 by 3 meters.
Yes, the unit becomes heavier and installation requires skill, but by every metric a double‑chamber IGU outperforms a single‑chamber one.
IGU formula
The next important point is choosing the right insulated glass unit (IGU) formula. The IGU formula refers to the combination of the following characteristics:
- glass thickness
- width of the spacer bars
To properly choose the formula, manufacturers provide special tables approved by standards. Glass thickness typically comes in 4, 6, 8, 10, and 12 millimeters. The choice depends on the size of the IGU.
The glass must be able to withstand wind loads. If you install thin glass in a large IGU, it will create a lens effect.
Glass bends under atmospheric pressure, and the image seen through it becomes distorted. In practice, this looks bad, and eventually, the IGU will have to be replaced with one that uses thicker glass.
Another important factor is the width of the spacer bar. Spacers come in 8, 10, 12, 14, 16, 18, 20, 22, and 24 millimeters. Narrow spacers should not be used in large-format IGUs.
The glass panes can bend so much that they touch each other. I’ve seen this happen on-site. I noticed purple stains that looked like smudges on the IGU and couldn’t understand where they came from. It turned out those were the areas where the glass panes were touching. Of course, this requires replacing the IGU.
The next, less obvious point: adjacent panes shouldn’t differ by more than a few millimeters—two at most. If one pane is 12 mm, the next should be 10 mm, and so on. Picture large and small window openings nearby: thin 4 mm glass in the small, 12 mm in the large. In reality this will look awful because the glass tint will differ dramatically. We’ll discuss this in detail below.
Regular or low‑iron glass?
First decide whether the glass will be regular or low‑iron. Regular glass has a greenish tint, especially noticeable at the edge.
On 4 mm glass the green hue is barely visible, but the thicker the glass, the more pronounced it is. Imagine a large double‑chamber IGU with three 10 mm panes—it will look completely green!
Чтобы такого не получалось лучше выбирать просветленное стекло. В составе обычного стекла — довольно высокий уровень железа. Оно снижает прозрачность и дает зеленый или голубой оттенок продукту. Глубокий уровень очистки исходного сырья от железа позволяет добиться практически идеальной прозрачности и высокого уровня светопропускания. У обычных стекол светопропускание примерно 83-89%, а у просветленных — выше 90%. Оно настолько прозрачное, что создает эффект отсутствия преград.
For your project, you can choose either three low-iron panes or a combination of different types of glass. It all depends on your budget. Some are okay with a greenish tint, while others are strongly against it. Low-iron glass is about 40–50% more expensive than regular glass. The good news is that there is production of this type of glass in Russia. It has a significant price advantage compared to European counterparts, which are much more expensive.
What coating will the glass have?
Modern technologies make it possible to apply silver and other metal particles to glass. This significantly improves performance.
Different types of coatings serve different purposes:
- Energy efficiency. This type of coating retains heat inside the building and prevents it from escaping outside.
- Solar protection. This coating reflects sunlight. It eliminates the greenhouse effect, preventing rooms from overheating due to the sun.
- Multifunctional coating. This type of coating both retains heat and protects from the sun. Naturally, this coating is very popular.
Energy-efficient coating should be mandatory! This type of coating significantly reduces heat loss.
As for solar protection, the higher its performance, the more reflective the glass will appear from the outside. Accordingly, multifunctional glass also reflects on the outside. For some people, this can be a downside. In my experience, I’ve had clients who were strongly opposed to the mirror-like appearance.
At the same time, multifunctional glass comes in a wide range of shades. It can be bronze, blue, green, neutral, and so on. There’s a lot to choose from, but be sure to check that the color rendering from the inside remains natural.
By the way, using multifunctional coating is a great way to eliminate the green tint without using more expensive low-iron glass. Thanks to its reflectivity and built-in color palette, it looks aesthetically pleasing.
How to choose the glass?
When choosing glass, samples are most often used. They can be small in size, but it’s much easier to evaluate the final look of the insulating glass unit using A4-sized samples. I recommend taking them outside to see how they look in the sunlight. That way, it’s easier to choose the shade you prefer, the level of reflectivity that suits you, and so on.
You can mix different types of glass and coatings to find the combination that works best for you.
Spacer bar
The last thing to decide inside an IGU is the spacer. Standard aluminum heats in the sun and creates a thermal bridge, so we now use warm composite spacers. They reduce heat loss along the perimeter and look better. After that come the primary and secondary seals.
You can choose between a standard aluminum spacer or a warm plastic spacer. The second option helps prevent condensation around the perimeter of the insulating glass unit.
Additionally, unlike the bright aluminum spacer, the plastic one can be made in any color. Most often, clients prefer dark frame shades, and a matching spacer color looks much better.
Glass safety
A very important point is safety. What happens if a large insulating glass unit breaks? Regular glass shatters into large sharp shards. This can be dangerous to life and health. That’s why it’s better to use tempered glass. When damaged, it breaks into small crumbs. It’s impossible to cut yourself on them—there are videos showing experiments where people squeeze this glass in their hand without leaving any marks.
I recommend installing tempered glass. At the very least, both the inner and outer panes should be safety glass.
For even greater safety, you can install laminated glass (triplex). Triplex is two panes of glass bonded together with a special film. Its high impact resistance ensures reliable protection.
But there are some downsides. First, laminated glass (triplex) is more expensive. It’s heavier and more difficult to install. There’s a risk of microcracks along the edges during installation or manufacturing. Over time, due to temperature fluctuations, cracks may appear—spreading across the entire surface. This doesn’t happen with tempered glass. Tempered glass is more likely to shatter entirely than crack. I once had to replace a large laminated unit several times due to such cracks. Technically, you can make triplex from two tempered panes, but in my opinion, it’s unnecessarily expensive. I believe tempered glass is the optimal choice.
I’ve covered the key points to consider when choosing an insulating glass unit. You should understand: the larger the glass unit, the thicker the glass needs to be. It’s harder to produce, transport, and install. Always pay attention to coatings and energy efficiency. The glass should be clear from the inside and maintain natural color rendering. And don’t forget about safety—tempered glass remains the best choice.
All these factors influence the price. The more panoramic the glazing, the more it will cost. If you want to optimize your budget, consider choosing smaller glass units and more affordable glass options.
You can always contact me for a consultation. I’ll help you choose the most optimal IGU for your project! With me, you’re guaranteed to get a price 15–30% lower than any market offer!
