What are the Key Differences Between Annealed and Tempered Glass?

Difference Between Annealed and Tempered Glass
Annealed and tempered are the two types of glass, each having unique properties and applications. This post provides a comparison between the two.
Did You Know?
Though tempered glass scores over annealed glass in the safety aspect, PPG recommends its usage only where necessary by code. This is because tempered glass is prone to spontaneous breakage and distortion which does not happen in case of the latter.
There are two manufacturing techniques referred to as tempering and annealing that are used to strengthen glass. The difference between the two methods lies in the way the heating and cooling processes are carried out on the glass, thus, resulting in two types of glass; namely, annealed and tempered.

There are two manufacturing techniques named as tempering and annealing that are used to strengthen glass. The difference between the two methods lies in the way the heating and cooling processes are carried out, thus resulting in the two types of glass by the same name.
What is Annealed Glass?
Annealed glass
This is a type of glass that is obtained by the process of annealing, wherein, hot glass that is formed is slowly cooled down to alleviate any internal stresses. If the glass does not go through the annealing process, it can be easily subjected to shatter or damage with exposure to a small temperature change or mechanical shock.
This is because many of the thermal stresses that occur due to quenching will be retained when not annealed, resulting in a significant decrease in the strength of the glass.
Window with table
Furthermore, when subjected to damage, they break into large, jagged shards that could cause serious injuries to any person or animal coming in contact. Thus, this type of glass is used in places where the risk of breakage and injury is less. It is most commonly and widely used for cabinet doors, tabletops, home window panes, and basement windows. A factor that contributes to its common usage in the market in spite of its fragile nature, is its low cost.
What is Tempered Glass?
Tempered glass
This type of glass, also known as toughened glass, is obtained by a process in which there is extreme heating of glass followed by rapid cooling. Due to tempering, the outer surfaces are put into compression and the inner surfaces into tension. As a result, this glass does not break into sharp shards when subjected to damage. Instead it would crumble into small granular chunks that have very less or no chance of causing injury.
Modern shower
Therefore, tempered glass can also be referred to as a safety glass that has been processed by controlled thermal or chemical treatments for increased strength. Since tempered glass is much stronger and safer as compared to normal glass, it has a lot of demand for usage in tub and shower doors, vehicle windows, refrigeration and food service equipment, glass doors with no frames, diving masks, etc.
Differences
Making
Annealed Glass

◼ It is slow-heated and then slowly cooled.
  • In this case, it aims at having very little tension.
  • It can be drilled, provided the right tools and techniques are used.
Tempered Glass

◼ It is superheated and then rapidly cooled.
  • Here, it aims at having quite a bit of tension in the center of the glass in order to give it strength.
  • It cannot be drilled.
Durability and Strength
Annealed Glass

◼ More Fragile
  • It is prone to breakage or damage.
Tempered Glass

◼ Higher in Durability and Strength
  • It can handle more wear and tear.
  • It is thicker and harder.
Price
Annealed Glass

◼ Lower Cost and Budget-friendly
  • However, due to higher probability of breakage, it may have to be replaced often.
  • This makes it costlier as compared to tempered glass if considered long-term.
Tempered Glass

◼ Higher Cost
  • The initial cost is high due to the longer process involved in its making as compared to annealed glass.
  • However, since it is known to last longer than annealed glass, it can be considered cheaper in the long run.
Safety Concerns
Annealed Glass

◼ Less Safe
  • On breakage, sharp and jagged shards can cause serious injury to anyone around it.
  • It can be used where the risk of breakage and injury is less and in low-traffic areas.
Tempered Glass

◼ More Safe
  • On breakage, small and granular pieces of glass are formed that do not cause harm.
  • It can be used in many places including high-traffic areas as it is tough and safe.
Even though tempered glass is valued for its safety and strength, if none of these factors are an issue, then annealed glass is a less expensive choice. Consider the aforementioned points and make the final choice as per your need.