Why Does Spark Plug Break Glass?

Asides from causing a spark that will ignite the engine, a spark plug is a great tool for breaking a car’s glass. Here’s all you need to know

In this article, I’m going to teach you all you need to know about why a spark plug breaks glass and how to break a window silently with a spark plug.

Now, looking at the physical features of the spark plug. It’s a threaded metal that’s used to connect the engine and cylinder which implies that it has the ability to withstand high temperatures and pressure from external forces.

This implies that a spark plug is capable of breaking a glass if enough force is been applied while hitting the glass.

This is also possible because a spark plug is made up of porcelain also known as aluminum oxide ceramic which accounts for most of its strengths.

Continue reading to find out further information as to why a spark plug breaks glass.

What Causes a Spark Plug to Break Glass

From the introduction above, it’s quite obvious that a spark plug is able to break through a car glass and other amorphous solids.

Here are a few reasons why this is possible,

1. A Glass is an Amorphous Solid

If you went to high school then you should be knowledgeable that glass is an amorphous solid which implies that they’re liquid in a cool state.

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Therefore the individual components can still move freely, unlike solids where movement is restricted due to the bonding.

So, once a spark plug which is metal is launched at a glass with a force greater than it can resist, the glass will eventually scatter.

2. Presence of a Ceramic Insulator on the Spark Plug

Ceramics are produced by introducing inorganic matter to high temperatures while an insulator is one that doesn’t transmit heat.

These features make the spark plug a bit hard and can cause damage if the right energy is applied to it.

As a result of this build-up, a spark plug seems to be heavier and rougher than other components of the same size.

3. The Force Applied

Finally, the amount of force extorted while projecting the spark plug towards the window also play an important part in the braking. This will give it more speed thereby shattering the glass.

4. Aim Position

It’s important to note that the middle part of a car’s glass is stronger than other corners of the glass.

If you aim at the middle of the glass with lower force, you might just get a crack on the glass without an actual break which will result in a second try.

How to Break Window Silently without a Spark Plug

I’ll advise that you do this in the case of an emergency and the only option to get into the car is by breaking through with a spark plug.

Talking about the silence part, it’s only a thief that’ll break into a person’s car silently, you could get into trouble.

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Nevertheless, here’s a step-by-step guide on how to break your car windows silently with a spark plug.

  1. Get a spark plug (new or old)
  2. You can decide to break off the electrode at the edge with a hammer
  3. Aim for the sides (preferably) or center of the glass and throw the spark plug with a force hard enough to break it.
  4. You can keep retrying all the angles till you get a breakthrough.

I’ll also add that there’s no way to break glass without making noise since it’s made with a mixture of silica sand and other particles in an undefined lattice system.


Q: Can a spark plug break a bulletproof glass?

No, bulletproof glass is built to restrict impact from forces as high as a bullet then what is a spark plug compared to it?

Bulletproof glass constitutes various layers of toughened glass and plastic that can resist high collision.

Q: Do Spark Plug Break Windows Silently?

No, there will surely be noise due to the individual components of the glass moving around unlike metals other parts will remain still even after the impact.

Q: What Causes Spark Plug electrodes to Break Off?

Reasons, why a spark plug electrode could break off, are

  • Incorrect spark plug installation
  • Unusual high temperature
  • Fault in the cylinder
  • Old Spark Plugs


If you’re wondering why a spark plug is able to break a car glass into pieces then this article is for you.

You’ve also learned how you can silently break a glass using a spark plug for free. Don’t use it for criminal acts.

Checkout > How To Cover A Broken Car Window

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