Home | Spark Plug | Why Does Spark Plug Break Glass? – 4 Reasons

Why Does Spark Plug Break Glass? – 4 Reasons

March 17, 2024 | Victor Lukasso

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

In this article, I will 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.

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

This implies that a spark plug can break a glass if enough force is applied while hitting the glass.


This is also possible because a spark plug is made 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

The introduction above shows that a spark plug can break through a car’s glass and other amorphous solids.

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Here are a few reasons why this is possible,

1. A Glass is an Amorphous Solid

If you went to high school, you should know that glass is an amorphous solid, implying that they are liquid in a cool state.

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

So, once a metal spark plug 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 insulators do not transmit heat.

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

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 plays an essential part in the braking. This will give it more speed, thereby shattering the glass.

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4. Aim Position

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

If you aim at the middle of the glass with lower force, you might get a crack on the glass without an actual break, resulting 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 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.

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.
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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 toughened and plastic layers that can resist high collision.

Q: Does 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


This article is for you if you’re wondering why a spark plug can break a car glass into pieces.

You’ve also learned how to break a glass silently using a spark plug for free. Please don’t use it for criminal acts.

Checkout > How To Cover A Broken Car Window

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.