What are the Key Differences Between Annealed and Tempered Glass?

Annealed and tempered are the two types of glass, each having unique properties and applications. Provided here is a comparison between the two.
Praseeda Shirodkar
Last Updated: Dec 05, 2018
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.
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.
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.
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.
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.
Differences
Making
Annealed Glass
It is slow-heated and then slowly cooled.
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.
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
More Fragile
- It is prone to breakage or damage.
Tempered Glass
Higher in Durability and Strength
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
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
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
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
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.