Find Out: Why Does Spark Plug Break Glass?

Why Does Spark Plug Break Glass

Did you know that carrying spark plug shards could get you in legal trouble? If caught, you would have to pay a hefty fine or stay in jail for a while! It is considered a misdemeanor as burglars often use spark plug chips for breaking into vehicles.

On the other hand, it could also be useful in situations where you are locked out of your car without its key; spark plugs can shatter tempered glass into pieces if thrown correctly. But how is this possible, and why does spark plug break glass? You will find all your answers by the end of this article.

Why Do Spark Plugs Break Tempered Glass Windows


The insulator of a spark plug is made from aluminum oxide ceramic. It is an extremely hard material and sharp fragments of the smashed ceramic, which can break tempered glass even when thrown with a little force. Spark plugs are also called ‘ninja rocks‘ due to their ease of shattering windows.

Almost all windows on a vehicle except for the windshield are made from tempered glass. While it is known to be strong, it is designed to shatter into small pieces for cutting down risks of injuries from a larger piece of broken glass. This is made possible by the way tempered glass is processed and manufactured.

How Tempered Glass Produced?


After the molten glass is shaped, it is cooled down to its solid state before further processing. Tempered glass is cooled very quickly from liquid to solid state. This allows the glass to have a lower density and a higher volume than other glass products cooled normally.

It also creates compression on the outer side and tension on the inside of the glass. In summary, tempered glass is hard and strong but has a huge amount of internal energy created by the compression and tension of the glass, which is caused during the tempering process.

Why Would Someone Want to Break a Car Window with a Spark Plug

Now that we have covered how spark plugs can break tempered glass windows, it comes to the reason why you might need to do it. Although a car window can also be broken with other tools such as a metal rod or a large stone, what would you do if you were stuck inside the car without these items?

A spark plug is just more accessible as it can be stored anywhere and can also be found at your nearest hardware store! Moreover, it is also very easy to break a car window by using a spark plug. If you are interested in knowing how to do it, continue reading to the next section.

How to Break a Car Window with a Spark Plug?


Before getting started, it should be noted that the entire spark plug is not required for this process. We just need the porcelain fragments of the spark plug’s insulator. You will need –

  1. A new or used spark plug
  2. (Optional) Hammer or any similar tool for shattering the spark plug’s insulator
  3. (Optional) Protective equipment to prevent injury from tiny ceramic shards

Once you have everything ready, follow these steps to break a car window –

  1. The first step is to shatter the spark plug’s insulator (the white part). If a hammer is available, you can smash it while holding the plug’s metal end, or you could smash it into a concrete floor, a brick wall, etc.
  2. Please pick up the pieces but be careful as they are very sharp. Use protective equipment if possible.
  3. Aim at the center or corners of the car window, and toss the piece(s).

If done right, the sharp edges of the porcelain fragments should create cracks in the tempered glass, and it will shatter almost instantaneously.

Safety Tips

To avoid a mishap, don’t stay too close to the window when tossing the ceramic chips. It could cause injury to you as the glass might break, or the chip may bounce back at you.

If somebody is inside the vehicle, ask them to move away from the targeted window.

Use protective gloves and eye goggles before handling the porcelain fragments if possible.


What is the weakest part of a car window?

A car window’s surface is weak near its edges and its center.

Do ceramic spark plugs break glass?

Yes, the ceramic insulator of a spark plug can be used for breaking glass. When thrown with a decent speed, it fractures the glass by concentrating the impact into small areas, which releases the glass’s internal energy and causes it to shatter.

What causes a broken spark plug insulator?

When an engine is knocking or misfiring, its pistons and valves overheat. It causes the electrode of a spark plug to enlarge, which in turn breaks the ceramic insulation.

Can a broken spark plug damage the engine?

Yes, and it is highly discouraged to drive a car with broken fragments from a spark plug inside as it may lead to serious damage or cause engine failure.

What liquid can break glass?

It is possible to break the glass by pouring hot water on it and immediately pouring chilled water. Due to a thermal shock, the glass will start to crack and break.

What is the white part of spark plugs made of?

The white part of a spark plug consists of an ‘electrode’ made from high-nickel alloys and an ‘insulator’ made from aluminum oxide ceramic.

Can porcelain break glass quietly?

While it is not absolutely silent, using porcelain chips to break glass is much quieter than using a hammer or other tools.


As you have seen, you can break a car window very easily with just a spark plug in case of an emergency. While it is used for unlawful conduct, it can also prove to be very useful in day-to-day life. With that being said, we hope to have helped you by answering why does spark plug break glass.

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