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What is the Difference Between Tempered Glass and Standard Glass?
Tempered glass and standard glass differ in the way they are processed. To manufacture any glass, sand, soda ash, and lime are mixed together and melted at very high temperatures. This hot liquid is formed into glass though blowing, pressing, or drawing. Once the glass is formed, it goes through an annealing process where it is reheated and cooled. This keeps it from shattering and restores its strength.
The annealing, or cooling process, is what determines whether glass will be tempered or standard. Tempered glass is forced to cool very rapidly, while standard glass is allowed to cool slowly. Cooling the glass quickly makes it stronger, so it can withstand at least four times the pressure of standard glass. It also reacts to breakage differently.
One of the most obvious differences between the two types of glass is how they shatter or break. Standard glass breaks into large, irregularly shaped, sharp shards. Tempered glass, on the other hand, shatters into small, evenly shaped pieces that pose much less risk of injury to those coming in contact with them.
Standard glass will break in the specific area of contact, resulting in cracks or a hole in one location, but leaving the rest of the pane intact. Tempered panes are more impact resistant, but shatter completely, leaving no intact areas. Because of this, they are preferred in applications where safety is important. Standard glass provides greater security, as parts of a pane can remain undamaged even after another section is broken.
Tempered glass is more heat-resistant and scratch-resistant than non-treated glass. Outwardly, however, it does not appear any different than standard glass. Both types of glass are made in varying sizes and thicknesses and can be colored or tinted.
Standard glass can be cut to size or pressed into shape after it is processed. If an application requires, its edges can be polished or holes drilled into it. Tempered glass cannot be reworked after it is tempered. Attempts to cut or drill into a pane would result in it shattering completely.
Because it is stronger and its fracture pattern safer than ordinary glass, tempered glass was once the standard for car windows and glass doors. In applications requiring the highest degrees of safety, laminate glass is now more commonly used. Laminate glass is formed by two layers of glass fused together with a layer of plastic in the center, producing a stronger glass. In situations of extreme force, laminate glass will crack, but it will not shatter.
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![Standard glass breaks into large, irregular shaped shards.]()
By: ivan kmitStandard glass breaks into large, irregular shaped shards. -
![Pieces of shattered tempered glass.]()
By: jayfishPieces of shattered tempered glass. -
![Standard glass is allowed to cool slowly.]()
By: FarawaysStandard glass is allowed to cool slowly.
Discussion Comments
I had a window installer tell me that my untempered windows cannot be tinted. He said that the tint will reflect the heat so intensely that it will shatter the glass. Is this true?
My cousin works on cars, and he told me that laminated glass is used for car windshields, but tempered glass is used on the windows. I'm glad that laminated glass is out front, because I would hate for the windshield to shatter every time a rock hit it! I seem to get hit with rocks a lot, but they only make a small dent that can be easily repaired.
A lot of older houses in my neighborhood have standard glass panes in their windows. I remember one old abandoned house that had a large shard missing on the door window above the doorknob.
This place hadn't been lived in for a long time. When we were teenagers, my friends and I decided to check it out.
I stuck my hand through the broken pane to open the door from the inside and I slipped and cut myself. I had a hard time explaining that wound to my mother!
@Kristee – I like the fact that my liquid measuring cups are made of curved tempered glass. The edges and the bottom are rounded, and the glass is extremely thick.
I can heat up liquids in them in the microwave without fear. Though the glass does get hot, it won't shatter.
I use tempered glass for safety when cooking. All my casserole dishes are made of this thick, heat-resistant glass.
I've heard horror stories of some glass pans shattering in the oven when someone opens the door because they can't tolerate the sudden change in temperature. While I would never move even a tempered glass dish from a hot stove to a sink of cold water, I don't feel the need to wince and brace myself every time I open the oven door.
@ElizaBennett - You don't say if it was one big piece of glass or just a pane, but if it was just a pane and you still have the door, I hope you've taken the time to buy tempered glass panes and replace *all* the panes in the door! You don't want the same thing to happen again.
Replacing a pane of standard glass with a pane of tempered glass is inexpensive and a fairly simple repair. You use a sharp knife to cut the glazing so that the old glass can be removed, sand down the frame, then install a new pane (cut to your exact measurement) and glaze it in place. You might need to re-paint afterwards.
Or just get a new, modern, energy-saving storm door!
I want to remind everyone that any glass doors in their home need to be tempered glass doors.
Tempered or other safety glass is now the standard, but this hasn't always been the case. If you live in an older home with an old door, it might contain standard glass - dangerous!
We found this out the hard way when my husband accidentally put his hand through a pane of glass in our decorative old storm door. (He was trying to "bang" it open, but it was latched.) It shattered under the (relatively light) pressure, and he cut himself.
But worse than the injury was the cleanup! Tiny pieces of glass flew all the way down our sidewalk. I was so afraid one of the children or neighborhood cats would find one that I missed.
Very helpful.
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