Why Do Spark Plugs Break Glass So Easily? (Explained!)

If you’ve ever seen a post on how to break glass, such as the ones in a car’s windshield or windows, you probably saw how easy to do such a thing with a spark plug. Thus, you may wonder if it’s true or if it’s just another trick. In general, it’s true, and you can find an explanation for that through this article. So, you may ask:

Why do spark plugs break glass so easily? Spark plugs break any glass so easily that a spark plug contains ceramic parts and the object that breaks the glass easily. In general, a ceramic object is much more complex than a glass. Thus, even with little force, it can shatter a glass, such as a car’s windshield or window.

Using spark plugs to break the glass is one of the common tips whenever you need to get in or out of the vehicle quickly. Since a simple punch or force in the glass won’t work, knowing that spark plugs can break a glass seems like a helpful tip.

In this article, you’ll see our in-depth take on spark plugs and why these auto parts can break windshields and windows with ease. This way, you can understand the reason behind it and get a sense of how it can happen.

Without further ado, let’s get into it!

Why Do Spark Plugs Break Glass So Easily

Why Are Spark Plugs So Great at Breaking Glass?

The first thing to note is that most of the windows are made of tempered glass. Tempered glass is famed for its strength, but it also breaks catastrophically, breaking into a vast number of tiny fragments in an instant.

In short, the windows’ glass is highly robust. However, due to the heating cycle, it has a significant quantity of internal energy stored. Its high energy makes it extremely sensitive to even minor damage from a spark plug’s ceramic component.

A sharp shard of the extremely hard aluminum oxide ceramic found in spark plugs concentrates the impact energy into a tiny, precise area. 

It does so without blunting to begin cracking. As a result, the force releases the internal energy, shattering the glass when hurled against a side window at a decent pace.

In a nutshell, it’s the ceramic part in a spark plug that creates enough damage to cause the glass to shatter.

Can a Spark Plug Break a Windshield?

Yes, a spark plug can break a windshield. The windshields of newer model vehicles usually come from laminated glass. 

While a strong type of glass can endure typical pressure, a tiny amount of force from a sharp small ceramic from a spark plug can easily shatter it.

One thing to note is that a spark plug has a ceramic part which is generally more robust than glass. So when you break the ceramic parts, they will get sharp edges.

With only a little force, the ceramic’s sharp edges can damage any glass that comes in contact with it.

Another thing to note is that the glass’ structure will get quickly shattered when the sharp but delicate edges of ceramic touch it. As a result, the glass will shatter into small cubes and break apart, which means no large particles will remain.

Now, since a ceramic part of a spark plug breaks glass so quickly, you may wonder if it goes the same with bulletproof glass.

Can Spark Plugs Break Bulletproof Glass?

While the ceramic part of a spark plug tends to work on a glass of windshields and windows, it may not work on bulletproof glass.

The thing is that the ceramic found in a spark plug tends to work only with tempered and annealed glass. Such types of glasses are the ones in windows and windshields. 

In general, most bulletproof glasses come from acrylic, polycarbonate, or even glass-clad polycarbonate.

If you want to break such kinds of glass, you’ll usually have to exert force, pressure, and damage on both sides. Still, even if you successfully do so, the glass of these kids doesn’t shatter easily.

What Makes a Spark Plug Break a Window?

The thing that makes a spark plug break a window is the ceramic part found in it. Spark plugs contain a ceramic part that is generally harder than glass found in a car’s window. 

Thus, even with a small amount of force, you can easily shatter or break a window with it. However, you’ll only need to break the ceramic part so it will have tiny sharp edges. 

Once those sharp edges contact the glass, it will cause immediate damage to the glass’ structure, causing it to shatter.

Since this glass is always under consistent pressure, it causes a chain reaction to the entire object.

This shattering is small particles of the glass that won’t likely harm or hurt anyone. For this reason, most people find the toughened glass in windows more ideal for safety than typical glass.

How to Break a Window With a Spark Plug?

If you want to break a window with a spark plug, you’ll need to get the ceramic part inside of it. Also, make sure it has sharp edges that can come in contact with the glass.

You can always take out the ceramic part by hammering down a spark plug until the ceramic breaks into a couple of pieces. But, unfortunately, even a tiny piece of ceramic can already cause a toughened glass to shatter. 

As mentioned earlier, window glass is usually made of toughened glass. The toughened glass has a structure that’s always causing pressure in the item per se. 

Thus, once a small ceramic part from a spark plug comes in contact with it, the slight damage it causes would create a series of damage until it shatters the whole glass.

In short, you only need to take out the ceramic part in a spark plug and throw it into the glass. Even a tiny amount of force is enough to shatter the window.

Spark Plug Window Break Mythbusters

If you’re thinking that the idea of shattering glass with a spark plug isn’t accurate, you may have thought about checking out if Mythbusters have tested it.

However, upon checking out, the only glass-shattering topic they had concerns a couple of methods, but it doesn’t include using spark plugs. It is a youtube video about that topic.

On the other hand, I’ve seen a youtube video about the said topic from National Geographic’s youtube video.

The idea about the video applies to how the ceramic particles in a spark plug shatter a window glass.

The same result happens, and it shows how easy it is for spark plugs to damage and shatter toughened glass found in a vehicle’s window.


In a nutshell, we can conclude that the spark plugs break the glass so easily because they include ceramic components, and it is the item that breaks the glass. A ceramic object is significantly more rigid than a glass thing. As a result, it may destroy glass, such as a car’s windshield or window, even with minimal effort.

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Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more