How to choose the right glass for PVC and ALU joinery – a guide for a smart decision

When buying new PVC or ALU joinery, most people focus on the profile, price and appearance. However, what has the greatest impact on warmth, noise and overall comfort in a space is actually — the glass.

Glass makes up the largest part of a window and it is what determines whether you'll be warm in winter, comfortable in summer, and whether your home will be quiet. That's why it's important to understand the basic terms and differences before making a decision.

You can have a top-quality frame, but if the glass is poor — heat loss will still be significant. Conversely, quality glass can significantly improve the overall performance of a window. In other words: glass is the "heart" of the window.

The Ug value shows how much heat passes through the glass — a lower value means better insulation, while a higher value means greater heat loss. For comparison, double glazing has a Ug of around 1.0–1.1 W/m²K, while triple glazing achieves around 0.5–0.7 W/m²K. This means triple glazing retains heat significantly better, resulting in heating savings — something you'll certainly notice during winter months, especially if you live in areas where temperatures drop well below zero.

Uw is the overall insulation value that includes the glass, frame and connecting elements. It is therefore always slightly higher than the Ug value. If you want a realistic picture of a window's energy performance, look at the Uw value.

The g-value shows how much solar heat enters through the glass. A higher g-value means more heat enters, which can be desirable for north-facing windows, while for south and west-facing windows a lower g-value is better to prevent the space from overheating.

LT indicates how much daylight passes through the glass — a higher LT means more light in the space, while a lower LT means a darker room. It's important to find a balance between sun protection and natural lighting, and if you're unsure what to focus on, our expert staff will answer all your questions and help you choose the ideal glass for your needs.

Double or triple glazing — this is the most common question we encounter. Double glazing is more affordable and sufficient for apartments and milder climates, while triple glazing offers better thermal insulation, better sound protection and lower heating costs. If you live near a busy road or in a noisy environment, glass plays a crucial role — although more panes don't automatically mean better protection, as the combination of thicknesses and layers is key, triple glazing is often recommended.

Low-E (low emissivity) glass has a special thin coating that reflects heat. In practice, this means it retains heat inside the space in winter, reduces energy losses and increases window efficiency. Although you can't see it, its effect is significant. Today it is practically a standard in quality joinery, such as ours.

Another question we frequently encounter is about the importance of the gas between the two layers of glass. Most commonly this is argon, which insulates better than air alone, thereby reducing heat loss. It gives particularly good results in combination with a Low-E coating.

For families with children, safety is especially important. For additional protection of household members and pets, laminated glass is recommended — it stays in place even after breaking — or tempered glass, which is more resistant to impacts.

For most homes and quality renovations, a good combination is triple Low-E glass filled with argon. The slightly higher initial price is justified by its characteristics, for which your home and family will be grateful.

Choosing glass is not just a technical detail, but a decision that affects everyday life — the temperature in the space, noise levels and energy costs. Quality glass is not an expense, but an investment that pays back through comfort and savings for years. The good news is that with a basic understanding of the terms you can make a smart decision and avoid the most common mistakes, and for all questions, advice and help in making the right decision, we are at your disposal.

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