Why Do Spark Plugs Break Windows? A Detailed Explanation

“Why do spark plugs break windows?” is a question on the lips of many car owners and enthusiasts. This question likely stems from the various clips of someone shattering a car window pretty easily using a spark plug. Well, it’s not just Hollywood magic, and there is actually a good reason why a spark plug breaks car windows.

Spark Plugs Break Windows ~ Ran When Parked

Read this complete guide for a detailed explanation of how this works!

Why Do Spark Plugs Easily Break Car Windows?

Spark plugs easily break car windows because they are generally made with porcelain, which concentrates a huge amount of energy at one point on the car window. While the process seems seamless, the spark plug still needs to be thrown with a moderate amount of force to break the windows.

Breaking a Car Window ~ Ran When Parked

Spark plugs are generally made with an aluminum oxide base, which many refer to as porcelain. While the primary role of spark plugs is to light the gas and air mixture in the engine by producing a spark, it has found a hugely important role in breaking windows.


And it does so quite easily, too, which surprises many, considering windows are designed to be tough.

The science behind spark plugs breaking windows so seemingly effortlessly is that the plug’s ceramic material concentrates a very high amount of force at one point of tempered glass. This force is sufficient enough to cause the glass to shatter upon impact.

However, it is imperative to apply enough force to the spark plug, as merely touching the windows will not cause it to break.

What Factors Affect a Spark Plug’s Ability To Break a Car Window?

The factors that affect a spark plug’s ability to break a car window are the ceramic insulating material, the density of the plug, and the speed at which it is thrown.

Spark Plug Ability ~ Ran When Parked

If these factors are not sufficiently met, the spark plug will not concentrate enough force to break the window.

Porcelain Insulating Material

Most spark plugs are made of an aluminum oxide or porcelain material. This ensures the plug has optimal heat conductivity and insulating ability. The choice of material is crucial to the spark plug being able to easily break tempered glass, as the ceramic can focus high force at a solitary point in glass.

Porcelain Insulating Material ~ Ran When Parked

Spark plugs that are made with other materials, like steatite, may not produce the same results as regular spark plugs. However, these types of spark plugs are extremely rare to find in modern vehicles.

Plug Density

The density of a material describes its mass per unit of volume, or simply, how tightly packed the particles in the material are packed. Therefore, density can be correlated to the heaviness of a substance.

Spark plugs have a very dense constituent material, and the implication is more weight and force being put on a specific area of a substance when it is thrown at that substance.

Throw Speed

The speed at which the plug is thrown is an overlooked yet critical factor that affects its ability to break a glass window. If the plug is not thrown fast enough, it does not gather enough force to break the glass. This makes sense, considering force depends on both mass and acceleration or velocity (speed).

While you don’t need hefty and muscular arms to generate enough force when throwing a spark plug, you still need to generate some amount of force. Therefore, just slightly hitting the plug on the glass window will not cause it to shatter.

How Can You Break a Car Window Using a Spark Plug?

You can break a car window using a spark plug by throwing the plug fast enough at a specific point of the window. As with any other process, there are steps to be followed to ensure that the car window shatters upon contact.

  1. Find a new or used spark plug. In emergency cases, you can use your car’s spark plug, which is generally near the top of the engine’s cylinder head. However, the more advisable option is to get one at a store and keep it in case you need to break a window.
  2. Break the insulator of the plug, which is typically white. You can do this with a stone, hammer, or similarly dense materials that can exert enough force to break the plug.
  3. After breaking the plug into smaller fragments, carefully throw the plug at the window.

Although you may need to throw more than one piece to break the window, if done right, you can shatter the window almost immediately on your first try.

What Are the Precautions To Take?

The precautions to take when breaking a window with spark plugs include giving a reasonable distance between yourself and the window. Also, you can never have too much protective gear, even while removing the plug and breaking it into smaller pieces.

Before you attempt to break a window with a spark plug, ensure you are not too close to the window. If you stay too close and the chip bounces back, you can risk obtaining serious injuries.

In some cases, although more uncommon, the glass may shatter so violently that shards may fly in different directions. In such cases, you want to be as far away as reasonably possible.

Aside from you, if there are individuals on the other side of the window, it is advisable to ask them to move away from the window before throwing. This also prevents them from any potential damage, especially with the glass breaking in that manner.

When trying to break the plug, you should wear protective gear. This includes gloves, masks, and glasses. Since you may not have the time to get these from stores in emergency situations, it is advisable to always have them in your home or workplace.

Where Is the Best Part of the Car Window To Aim the Spark Plug?

The best part of the car window to aim the spark plug is the edge or center of the window. This is due to the manufacturing process of the glass used for windows. Between the two spots, the edges are the weaker parts of the window.

Best Part of the Car Window ~ Ran When Parked

Although these spots are structurally the most culpable to fracture, you can actually break a car window from any point. In fact, you may even get it on the first try if you generate enough force behind the plug.

What Are the Possible Reasons for Breaking a Window With a Spark Plug?

The possible reasons for breaking a window with a spark plug typically revolve around its ease and convenience compared to other tools like crowbars and hammers. Also, spark plugs are much more handy and readily accessible, as they can be easily kept inside the car.

Possible Reasons for Breaking ~ Ran When Parked

Given the science behind breaking a window with a spark plug, you can deduce that any substance that can also concentrate high amounts of force at a point can break a window. This includes dense materials like hammers and metal bars. However, none of these substances are as convenient to use as a spark plug.

Also, in emergency situations where an individual is trapped inside a car, it will be almost impossible to access a large stone or a metal bar. In such cases, it will be much easier to find and use a spark plug.

Frequently Asked Questions

Can Spark Plugs Break Bulletproof Glass Windows?

No, spark plugs cannot break bulletproof glass windows. This is because these windows are specially designed to withstand colossal amounts of force and consist of multiple layers. No matter how fast you throw the plugs at glass windows, it will be an effort in futility.

Bulletproof Glass Windows ~ Ran When Parked

If you need to break a bulletproof glass, you will need to repeatedly shoot at the same point. Even then, the glass may still not shatter for hours. No matter how good your throwing skills are, you cannot throw faster than a bullet.

Any effort to shatter the bulletproof glass may actually result in injuries to you from the rebounding of the plug.

Do Car Windows Make Noise After They Are Broken by a Spark Plug?

No, car windows do not make noise after they are broken by a spark plug in most cases. The car window is designed to absorb the impact of the material in contact, and if the force is strong enough, the glass simply shatters without making a noise.

What Are the Potential Dangers of a Broken Spark Plug in a Car?

A broken spark plug in a car can have serious consequences. It can lead to engine misfires, poor fuel economy, and even engine damage. If left unaddressed, driving with a broken spark plug can result in costly repairs and decreased performance while driving with blown head gasket can result in engine failure and potential safety hazards.


Car windows are designed to be durable and withstand force, yet they are so easily broken by spark plugs. Here are some of the main points from the article:

  • Spark plugs are effective in breaking car windows as they can concentrate enough force on one point of the glass.
  • The factors that determine a spark plug’s glass-shattering ability include its density, speed, and the ceramic used in its manufacture.
  • The best point to throw spark plug pieces is the edge or center of the window, as those are its weakest points.
  • Ensure you are in protective accessories when attempting to break windows with spark plugs, as well as not staying too close.

Now, you know exactly what to do if you have to break a car window next time!

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