The Types of Glass We Use – Part 1

Here are Miller Window, we use high-quality glass manufactured by PGT. We offer a wide variety of glass types to suit specific needs.


Annealed glass is the result of a cooling process that glass undergoes after being produced in the PGT factory. A piece of glass has to be cut in its annealed form, prior to undergoing additional processes such as heat-strengthening or tempering. Once a piece of glass has been heat-strengthened or tempered, it will shatter if cut.

On a strong impact, annealed glass will break into large shards.


Once annealed glass is heated to approximately 1300°F, where it reaches its softening point, it becomes heat-strengthened glass. This glass is then cooled to create surface compression. Surface compression allows the glass to tolerate more rapid and uneven temperature swings.

A major benefit of heat-strengthened glass is that it is twice as strong as annealed glass. However, if it receives a strong enough impact, it will break into medium-sized pieces.


For insulating glass, a special silicone glazing process is done to help keep the glass from breaking away from the frame. Insulating glass is composed of two panes of glass separate by air or other gas to help reduce heat transfer.

This extra space of insulations helps to prevent heat loss from a home and increases energy efficiency.


Laminated glass is also silicone glazed to prevent it from breaking away from the frame. With laminated glass, two pieces of glass are bonded together with a strong, clear interlayer. Once sealed, this glass “sandwich” behaves as a single unit and is transparent like ordinary glass.

Laminated glass provides and extra layer of protection against noise and harmful UV rays.

Laminated Insulating

This type of glass combines the benefits of both laminated glass and insulated glass.

The special silicone glazing process is done to keep the glass from breaking away from the frame. A window of this type is composed of three panes of glass: two panes bonded together with a strong, clear interlayer for impact resistance – the laminated glass – and another pane with space in between – the insulating glass.

Laminated-insulating glass is both strong and energy efficient.


The process of creating tempered glass is similar to heat-strengthened glass: annealed glass is heated to approximately 1300°F. Tempered glass, however, is cooled more rapidly which creates higher surface compression. This makes the glass much more resistant to blunt impact and even more tolerant of temperature swings than heat-strengthened glass. A pane of tempered glass is approximately four to five times stronger than annealed glass.

Tempered glass is also commonly called “safety glass”. That’s because, if something manages to break it, it will shatter into many small, blunt pebble-like pieces that are less of a cutting hazard than the sharp shards that many other glass types break into.

In our next post, we’ll discuss the different glass thickness, energy efficiency, and tints that we offer with our products.