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Image source : pinterest

The first picture depicts the glass that is found from an accident site, while the second picture depicts the glass that we use in our home.

What is the difference between these two glasses? Why doesn't the first glass, which is used as a wind shield in vehicles, breaks like the glass that we use in our home?

  • 2
    $\begingroup$ The first is prestressed, or tempered glass. It is designed just for that purpose: to break in a relatively safe way. $\endgroup$ Mar 13, 2018 at 7:14
  • $\begingroup$ Related: chemistry.stackexchange.com/questions/38922/… $\endgroup$ Mar 13, 2018 at 10:56
  • $\begingroup$ BTW, in most countries windshields (windscreens) may not be made of tempered glass, though side and rear windows, because even minor damage causes the glass to suddenly disintegrate. $\endgroup$ Mar 14, 2018 at 23:57
  • $\begingroup$ In the US, glass in exterior doors and showers and some others are also tempered glass. ( I have swept up 2 windows from doors.) $\endgroup$ Oct 5, 2018 at 20:44

1 Answer 1


Let's start out by covering the


Glasses used in automobiles are designed to break in tiny pieces.
Imagine you're driving down a dark highway hitting dangerously high speeds and then suddenly you lose control and crash.

If the glass used was not to shatter in tiny pieces rest assured you would not remain in one piece. Essentially it shatters for safety reasons.

Household glass on the is generally not involved in such drastic accidents so there is no need for it to shatter into tiny pieces .

How is it done?

From How Stuff Works

Tempered glass is created by heating and then rapidly cooling the glass to room temperature by ushering it through a system of blowers. The surface of the glass cools much faster than the center of the glass and contracts, causing compressive stresses, while the center of the glass expands because of its temperature, producing tensile stresses. What does that mean? Imagine a piece of glass that could be pulled or stretched to a certain length (tensile stress), while being pushed down and compressed (compressive stress) simultaneously. Both the pulling and pushing stresses achieved through the heating and cooling process give tempered glass its tensile and compressive strength. The differences between these two give the glass 5 to 10 times the amount of strength it originally had.

This system holds a lot of energy due to the stress so when it breaks all of it is released causing the glass to shatter into tiny pieces


Automotive glass contains more energy than normal household glass. When it breaks all that energy is released which causes the glass to break into tiny pieces.

  • 4
    $\begingroup$ Mostly right, but an automotive windshield is also laminated to reduce the risk of injury. $\endgroup$
    – MaxW
    Apr 1, 2018 at 19:32

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