Window Glass: features, parameters, tips on how to choose the best

Types of glass for windows: differences and advantages

Choosing the right type of glass is one of the most important aspects of designing a window, as it directly affects thermal insulation, indoor comfort, natural lighting and safety. Here are some of the most common types of glass for windows and doors:

1. Low-emissivity glass (low-E glass)

This glazing is treated with a special metallic oxide coating that drastically reduces heat loss to the outside, without compromising natural light entry. These low-emissivity treatments allow the glass to retain up to 90% of the heat generated indoors, making them especially efficient in winter and ideal for improving energy savings.

2. Solar control glass (selective glazing)

Also known as solar-selective glass, this type of glazing is designed to filter solar radiation. It limits heat gain during the summer while maintaining high light transmittance, making it ideal for south-, east- or west-facing facades more exposed to sunlight. By reducing overheating, it helps lower the use of air conditioning and improves energy efficiency.

3. Thermal glass (insulating glass)

This type of glass consists of two or more panes separated by a sealed space filled with noble gases. Thanks to its low thermal transmittance (Ug-value), it offers excellent protection against heat loss. In triple-glazed windows with double cavities, the Ug-value can be as low as 0.6 W/m²K, significantly boosting insulation performances.

4. Safety glass (anti-breakage glazing)

Designed to enhance passive security, this safety glazing is made of multiple sheets bonded together with PVB interlayers. In the event of an impact or break-in attempt, it does not shatter easily and can resist strong blows, thus offering the maximum protection.

Insulating glass composition and number of panes

The insulating glass unit, commonly referred to as double glazing or triple glazing, is the technological core of modern windows. It’s designed to deliver high thermal and acoustic performances by using two or three panes of glass, separated by one or more spacers and sealed airtight, in order to form cavities filled with air or gas.

• Glass panes: in the most common configuration the unit includes two panes of glass, but triple glazing windows with three layers is increasingly popular for its enhanced insulation capacity. Each pane can be treated with low-emissivity or solar control coatings to further improve energy efficiency.
  
• Spacer bar (warm edge spacer): between the panes, a spacer bar (usually made of thermally insulating material) defines the width of the cavity, keeps the panes properly aligned and helps minimize thermal bridging along the edges.
  
• Insulating gas: the cavity between the panes is not empty nor filled with regular air. Instead it’s injected with a noble gas such as argon, which has low thermal conductivity and improves the window’s average thermal transmittance.
  
• Surface treatments: the glass surfaces can also be enhanced with magnetron coatings — ultra-thin metallic films that control solar gain and reduce heat loss, while still allowing plenty of natural daylight.

Why not just use one thick pane? The answer lies in thermal physics: a single thick pane doesn’t insulate nearly as well as two or three panes separated by a gas-filled cavity. It’s the cavity and the gas layer between the sheets that efficiently act as a thermal barrier.

Solar factor and light transmission: what you need to know

Window glass isn’t just about insulation from cold — it also needs to manage how light and solar heat enter your home. Two key performance indicators help guide this choice: solar factor and light transmission. These parameters are essential when selecting the right type of glazing for windows, based on your home’s orientation and climate.

The solar factor (Fs) represents the percentage of solar energy that passes through the glazing and enters the building as heat. A high Fs value means more solar energy is transmitted — ideal for colder climates or north-facing windows where passive solar heating can be beneficial. Conversely, a low Fs helps block excess heat, making it suitable for south-, east- or west-facing rooms in warm climates where overheating is a concern.

Light transmission (TL) measures the amount of visible daylight that passes through the glass, excluding heat: the higher the TL, the brighter the room will be. Glass with high light transmission is perfect for dark or shaded spaces, while lower TL glazing helps reduce glare and control brightness in sunny areas or rooms with large glazed surfaces.

Thermal transmittance: how to improve glass insulation

When it comes to windows and glass frames, one of the most important performance indicators to understand is thermal transmittance, as it reveals how well a window can insulate a room from heat and cold, directly impacting comfort and energy efficiency.

The thermal transmittance of glass, known as the Ug-value, measures how much heat passes through 1 m² of glass for every degree of temperature difference between the indoor and outdoor environments. It is expressed in W/m²K and the lower the value, the better the thermal insulation of the window. For example:

• A single pane of glass has an average Ug-value of about 5.8 W/m²K;
• A modern double-glazed window can reduce it to 1.1 W/m²K;
• A triple-glazed window filled with insulating gas can reach as low as 0.6 W/m²K.

Why choose a low-Ug glass for your windows?

• To enhance thermal comfort — minimizing heat loss in winter and heat gain in summer translates to lower energy consumption and bills.
• To qualify for government incentives or tax deductions available for window replacements, as long as the new windows meet local regulatory limits.

Cleaning and routine maintenance of window glass

Proper maintenance of window glass is essential to preserve both the performance and appearance of your windows over time. Here are a few simple but effective tips:

1. Initial cleaning after installation: remove any adhesive labels or protective spacers shortly after installation. Clean the glass surfaces with a soft cloth and glass-specific cleaners to prevent residue from sticking permanently.
2. Regular cleaning routine: to keep your double-glazed windows crystal clear and functional, it’s recommended to clean them at least every 3 to 6 months using neutral detergents, lukewarm water and microfiber cloths. Avoid harsh chemical products or ammonia-based cleaners that could damage the glass or any special coatings.
3. Don’t overlook the details: make sure to also clean the spacer bar and edges of the glass, where dirt tends to accumulate. If your insulating glass units include integrated blinds or pleated shades, check periodically to ensure they are working properly.

A consistent maintenance routine not only keeps your windows with double or triple glazing looking great, but it also helps prevent surface clouding, maintains thermal insulation performance and ultimately extends the lifespan of your windows.

Professional installation: how it makes all the difference

Installation is just as important as choosing the right type of glass or frame material, since a properly fitted window guarantees long-term performance, comfort and efficiency.

Why is professional installation so essential? Here’s why:

• It prevents thermal bridging and infiltration of air or water;
• It ensures the certified Ug-value of the glass and the transmittance of the window;
• It maintains optimal functionality over time, ensuring easy opening and closing;
• It contributes to healthier indoor environments and consistent thermal comfort.

DQG, a leading Italian company with over 50 years of experience in the window and door industry, offering a wide range of Made in Italy uPVC and uPVC/aluminium windows and doors, fitted with high-performance insulating glass for maximum durability and security.

Our technical team follows the strict standards of the PosaClima certified system, ensuring peak performance in every context — residential, public, social housing, civil and industrial. Thanks to our quality certifications, every window installation complies fully with the latest regulations on energy efficiency and indoor wellbeing.

Choose DQG for your new windows and doors, combining comfort, insulation and quality!