Window Panes: Different Types of Glass and Coatings

Window Panes: Different Types of Glass and Coatings

After deciding on the type of replacement window, the next step would be determining the right glass or coating for it. Choosing the glass is often overlooked in a window replacement project. Well, it’s understandable since most homeowners just think that glass is just glass. It’s a transparent material that usually has no color, style, or design. But you may be surprised to know that there are different kinds available on the market, with each one designed for a certain purpose.

When choosing the glass for your window, there are many factors you need to consider. It typically depends on the location, climate, features, and design that you have or prefer. Each one is made and treated differently, affecting its strength, appearance, and energy efficiency.

With the various options that you can choose from, it can be overwhelming and difficult to find the right kind. To help you understand more about glasses in windows, here are different types of glass and coatings so that you won’t have to research them one-by-one. 

Float Glass

The most basic of the glass types is the float glass. The term ‘float’ refers to the process of how it is made. This glass is created by floating molten glass on a tin to form thin, large, and flat glass panels. It often produces a standard smooth sheet of glass of consistent thickness. 

A float glass is typically used as a starting material for a window. It will be used to create different types of glass because alone, it is very fragile. This is because it has not yet been treated, cut, or installed into a frame. It is inexpensive, but you wouldn’t want to use a weak glass for your window. When used as is, it will easily break and produce shards, which can be harmful.

Annealed Glass

The next step that a float glass goes through is typically annealing. It is a slow and controlled process used to strengthen the glass. It makes the panel more durable after reducing the internal stresses within the glass by quickly cooling it. 

A float glass also goes through this process so that it can be further upgraded or treated. Annealed glass isn’t commonly used in buildings because it will produce large, dangerous shards when it gets broken. That’s why it’s not enough to use the glass after annealing.

Heat Strengthened Glass

To make annealed glass stronger, it goes through another process which will make it heat strengthened glass. This type is made by reheating the annealed glass around 1200 degrees, which is higher than its annealing points, and then quickly cooled.

This will make heat strengthened glass twice as tough. But even after the annealed glass has been turned into heat strengthened glass, it still won’t be good to use alone in exterior windows. It is more durable, but it is still in the lower grades of window glasses. Plus, it can still break into sharp but less dangerous shards, since it will be smaller than the shards of annealed glass.

To use this for exterior windows, it needs to undergo another process and become a laminated window. But before we discuss this type, let’s talk about another way to make annealed glass stronger.

Tempered Glass

Similar to heat strengthened glass, tempered glass also follows the same process of heating and then cooling. But what makes tempered glass different is that it makes annealed glass four times stronger. This is because it is cooled more rapidly than heat strengthened glass. 

Considered as safety glass, tempering is the process of heating the annealed glass to 1200 degrees and rapidly cooling it. The internal section of the glass will be fluid, which will allow an equal amount of compressive and tensile stress to form more equally across the panel. 

Tempered glasses are also subjected to heat soaking, which is a method to test if the glass is stable. Some glasses have unstable nickel sulfide inclusions, which can cause the pane to suddenly break. To check if the tempered glass is ready to be used in the field, it is placed in an oven and heated to 550 degrees for a couple of hours. The unstable nickel sulfide inclusion will then expand, causing the glass to break. If it is stable, the glass won’t get broken and can now be used in real-life applications. 

Note that this type can’t be cut,  so the annealed glass should be cut and finished in the preferred size or shape before tempering. While it is stronger than float glass and annealed glass, it can still break from strong impact. This can also break into shards, but it would be smaller and less harmful. That’s why some buildings have tempered glass for big or low windows, especially in busy areas. Since it is durable but still breakable, it can be used as an emergency exit.

Laminated Glass

Another type of safety glass is laminated glass. It is formed by combining at least two float glass panes with a layer of polyvinyl butyral (PVB) resin in-between. The glass and interlayers of PVB are then fused using high heat and pressure to create an extra-strong panel.

It is also considered a security-enhanced glass because laminated glass stays in the frame even when it gets broken. This makes it suitable for those who want durable glass for safety and security reasons. The glass won’t break into dangerous shards and won’t leave the window open for potential threats to get inside the house. This is because the broken glass will stick to the PBV resin layer, staying in place.

You’ve probably seen this glass since it is also used in windshields. It is an important type in the automobile industry because, in an event that a vehicle collides with another one or against an immovable structure, the glass won’t break into shards and harm the driver and passengers. 

However, this only applies if the panes are heat-strengthened glass. This type won’t allow an object to pass through as well. If it is made out of tempered glass, then the glass will still fall out but not into shards. The PVB interlayer will still hold it together, resulting in one broken piece - looking like a broken mobile screen. This type is also used in vehicles but in the side windows. This is to allow the people to break the glass and get out of the car in an event of an emergency.

Impact-Resistant Glass

Also called hurricane glass, this type is suitable for those in regions with inclement weather. If your home needs storm protection, then this glass was designed to withstand strong gusts or hurricane-force winds. It can also prevent flying objects from shattering the windows or breaking into the house.

Similar to laminated glass, hurricane glass has an interlayer to keep the glass in place. It will only be stronger to help prevent rain and air from entering the home even if the glass gets broken. Even if you’re not in a hurricane-prone area, you may want to use this type of glass if you live near golf courses, parks, or stadiums.

Obscured Glass

If you need to find the right glass to improve privacy, one of the most common options is the obscured glass. This type cannot be clearly seen through but it will still allow light to come in. It is because the glass has designs or patterns, which can be coated, etched, beveled, or frosted to make it less transparent. If you look through it, you’ll just see the shadows or outline instead of the details.

Obscured glass is typically used in bathroom windows and side windows in entryways. While it may still allow light to pass through, it lessens the amount of natural light that can come in. It will also affect the outward view.

Tinted Glass

If you want some privacy but still have natural light come in, another alternative is tinted glass. Also called colored glass, it won’t block as much as obscured glass, but it will still decrease the inward visibility.

As you know, glass is clear and transparent. To make it less see-through, tinted glass is any type of glass that has been colored. Aside from increasing privacy, it is also used for aesthetic purposes. While it can be used for the whole pane, some use it for stained glass windows, typically as an internal window.

This glass can also be used as protection against UV rays. But it won’t be durable unless toughened or laminated. It should be processed properly if it is to be used for safety and security reasons. 

Mirrored Glass

If you’ve watched crime films or shows, you’re probably familiar with the interview room with one-way glass. This is also known as a mirrored glass, which is another type you can use for more privacy.

To create this glass, one panel is coated with metal and protective sealant, which creates the “mirror.” It is also used for decorative purposes, usually for internal windows, walls, doors, and furniture. 

If you do use it for exterior windows, you’ll decrease inward visibility while still having your outward view. It can also reduce heat gain since the glass will be able to reflect some sunlight. This means it will compromise the amount of light that can pass through, which is not suitable for those who want a certain amount of natural light inside their home.

Do note that the “mirror” effect may not be the same at night. When the light is turned on inside the house while the outside is dark, the windows can be seen through. You’ll need to install some curtains and blinds or apply a different treatment or coating. Similar to tinted glass, you will also need to toughen or laminate for safety and security purposes.

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Kenneth Wilson
December 28, 2020
Window Replacement

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done.