Why Is There Mold On The Styrofoam In The Air Conditioner?

If there is one visitor that is not welcome in your home, it’s mold. It grows in dark and damp areas and releases spores to spread across your home. Different mold spores circulating in the air are not only a pain for your respiratory system but also a nightmare for your overall health. That’s why you should always breathe fresh and clean air. This article will go into the question: why is there mold on the styrofoam in the air conditioner.

Being a sterile material, you would think nothing can grow on styrofoam. The substance has no nutritional value or any ability to absorb moisture means it is perfectly mold-free. 

But if that’s true, then why do you have mold growing on your window air conditioner’s styrofoam? Scroll down to find out why.

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Why Does Styrofoam Get Mold?

Air conditioners use styrofoam as a sealant to keep inside air from escaping outside. Unlike common insulators such as cellulose and fiberglass, styrofoam is highly resistant to mold. 

However, if your AC lies out in the open, it can quickly accumulate dust and moisture, and become dirty. And if the conditions are ideal, mold spores quickly start growing on your appliance before you can do anything about it.

Mold growth mainly depends on the humidity of the air surrounding it. If it is hot and there is no airflow, your AC’s styrofoam can become the perfect breeding ground for mold.

Moist and Damp Environment

All living things need a source of nutrition and a constant supply of (a small amount of) water to enable growth. 

In the same way, mold also needs an ample amount of water and food to germinate its spores. 

In humid climates, there is no shortage of water in the air. This moisture can penetrate porous surfaces, making it easier for the spores to anchor themselves in the material and start their growth. 

However, styrofoam is not porous or easily penetrable to water. That is why fungi find it challenging to sink their roots into this surface. This is true unless the material is flooded for a long time, such as in the case of floods. Here, mold can grow on an otherwise sterile surface.


While fungi can get water relatively easily from their surroundings, they also need a constant source of nutrition to aid their growth. But that isn’t too hard for common black mold, which feeds on easily available dirt and plant matter.

These fungi devour cellulose that is found in all plants as well as materials made from plants. Other than this, mold also feeds on hair and soil in the dirt, meaning that if your air conditioner has been collecting dirt and debris over time, you have a high chance of getting mold on the styrofoam insulation.

Additional Issues

The good thing about styrofoam is that it’s mold-resistant under normal conditions. The bad thing, however, is that mold can still grow on it, under special circumstances. 

In nearly all cases, problems with mold on styrofoam occur following a natural disaster or destruction that compromises the integrity of the insulating material. Flash floods and heavy rains can cause moisture and dirt to accumulate. As a result, mold thrives on the surface of the material.  

Is It Safe To Use an Air Conditioner With Mold Growth On Styrofoam?

Given how awful mold growth can be, it doesn’t impact your air conditioner’s performance. That means you can still operate it like normal, even when the styrofoam is covered in fungi. But just because you can use it, doesn’t mean you should.

Although mold growth may not impact your AC’s cooling ability, using the unit when there is mold present in it is quite unwise. The microscopic mold spores from the fungi on the insulation will circulate around the room with the air from your air conditioner. As time goes on, breathing in these tiny spores can cause damage to your lungs and respiratory system. Hence, it is not worth the risk.

Should I Remove The Styrofoam From My Air Conditioner?

If you’re thinking of getting rid of the insulation in your window AC is a good idea to solve the mold situation in your home, you must stop in your tracks!

The white foam is an integral part of the appliance and should not be removed. Typically, this part will need to be replaced by a qualified technician in case it needs a change.

How Do You Get Mold Out Of an Air Conditioner with Styrofoam?

For folks who are tired of the mold growing on the styrofoam in their AC, here are a few simple steps to get rid of the fungi problem.

Warning: the styrofoam in window air conditioners is there simply to close off the gaps that exist between the frame and the air conditioner itself. Without this styrofoam, the air conditioner won’t function properly. Therefore, make sure you don’t damage it while you follow the steps below.

  • Firstly, you want to turn off your air conditioner and unplug it too. It’s generally a good habit and also a necessary safety measure for whenever you’re working with electronic equipment. Therefore you must cut the power supply for your window AC as well before you begin treating it.
  • Next, carefully take out the styrofoam from the window AC. Clean it thoroughly from every angle to eliminate the dirt buildup out as much as you can.
  • When it comes to cleaning the styrofoam, most of the time you are going to need only a piece of cloth that you can dampen in water. Use the cloth with some cleaning agent spray and that should take care of the regular dirt that covers the styrofoam.
  • This won’t be enough for mold obviously. For that, you can try working with undiluted vinegar as it is an effective household cleaner and disinfectant. 
  • For deep cleaning, you can soak your window AC’s styrofoam in water and add an industrial cleaning agent into the water creating a mixture for deeper cleaning.
  • Depending on how grimy your AC styrofoam is, you’ll have to soak it twice or thrice even. When you are satisfied with the cleaning, you can let the styrofoam dry out for a while before putting it back in.
  • Once you have cleaned the styrofoam and dried it out, it’s time to put it back in between the frame and window AC. Make sure not to leave any gaps while reinstalling the styrofoam.

Related article: How to Kill Mold with Temperature (Heat and Cold Treatment)

How Do I Prevent Mold in My Air Conditioner?

Let’s face it, no one wants disgusting black mold growing in their home. Thankfully, there are several preventative tips that can help you fight and limit the growth of mold and other fungi on the styrofoam in your air conditioner.

1. Move Your Air Conditioner

Found mold and fungi on the inside of the air conditioner? 

We already know mold loves the dark, humidity, and nutrients. The puzzle you have to solve here is how the water and dirt got inside your AC. 

If your cooling appliance is located in the shade of a tree or in an area with lots of soil and debris, dirt can quickly build up in the AC. The only way to prevent mold from growing back onto the insulation, in this scenario, is to move it to a cleaner location. With no more nutrients to feed on, the mold will perish and stop growing. 

2. Inspect For Mold Before Use

It’s good to check your AC unit for signs of fungi growth if you recently took it out of storage. Whether we’re talking about a storeroom, attic, or basement, all these areas are usually dark, covered in dust, and have high moisture due to being closed all the time. 

Therefore, before you turn on your air conditioner, get it checked and cleaned by a professional to be on the safe side.

3. Use Mold Inhibitor

Using mold inhibitors can prevent mold and mildew growth in your air conditioning system. Spray or wipe your cooling system with the mold inhibitor chemical on each component according to the directions on the label.

4. Try A Disinfectant

The first step before treating your air conditioner styrofoam with a mold inhibitor is to treat it with a disinfectant. For this, choose an AC-safe disinfectant endorsed by the Environmental Protection Agency (EPA) so you don’t end up damaging your AC unit.

5. Drill Drainage Holes

If your air conditioner is susceptible to pooling water inside, consider drilling a few holes in the casing to tackle the issue. Small 3/8 inch holes can facilitate water to escape the body of your air conditioner, making sure there won’t be any moist feeding mold inside.


As annoying as it is, mold can develop on any material if given the right circumstances. But with regular cleaning and removing dirt from your AC, you can stop the mold and mildew from taking over the styrofoam in your cooling system.

With some thorough cleaning and precautionary measures such as spraying with mold inhibitors or adding a few drip holes, you can remove any chance of mold and fungi growing on the Styrofoam in your window AC.

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