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How to Waterproof Styrofoam?

Purchasing styrofoam insulation for your home is a great way to improve the energy efficiency and keep your home warm during the winter. However, if you are not careful, water can seep into the foam and cause damage.

In this guide, we will teach you how to waterproof styrofoam so that it can withstand any weather conditions. We will also provide reviews of the best products on the market to help you make an informed decision. Let’s get started!

How Waterproof Is Styrofoam?

If you are using standard white styrofoam blocks, they will likely float for a while but eventually absorb water and sink. However, if you are using expanded polystyrene foam (EPS), also known as beadboard, it is much more waterproof.

How Waterproof Is Styrofoam?

Beadboard is a great way to keep your house dry. This foam is made of tiny beads that are fused together. The blowing agent creates air pockets in the foam, making it resistant to water absorption. It is very durable and can stay in shape for a long time without breaking.

The downside to using beadboard is that it’s not as strong or durable as standard Styrofoam. The material can easily be dent or crushed, so it is not the best choice for applications where impact resistance matters most.

The durability of extruded polystyrene foam makes it a good option for use in kitchens. The larger beads make the board stronger and more resistant to impact than other types, such as Beadboard that can be found at your local hardware store or even online!

XPS is a little more waterproof than beadboard, but it is not much different. It will still absorb water over time if left underwater.

So, if you’re looking for the most waterproof option, beadboard is your best bet. But if you need something stronger and more durable, XPS is a better choice. [1]

How to Waterproof Styrofoam?

There are two types of Styrofoam: extruded polystyrene (XPS) and expanded Poly Satin Foam (Eps). It is important to know which type you have so that we can work with it properly!

Extruded polystyrene foam is a type of insulation that is commonly used in construction. It is white and has a smooth, shiny surface.

Expanded polystyrene foam is a type of styrofoam that is often used for packaging.
It is often referred to as “Styrofoam.” It is white and has a rough, uneven surface.

EPS can be further divided into two types, bead board and block form.

Bead board is made up of small Styrofoam beads that are fused together. It is lightweight and has a smooth surface.

Block form is made up of large blocks of Styrofoam that are cut to size. It is heavier than bead board and has a rough surface. The type of styrofoam you have will determine the best way to waterproof it.

How to Waterproof Styrofoam?

Extruded polystyrene foam can be waterproofed with a product called XPS Foam Sealant. This is a liquid that you put on the surface of the foam to form a waterproof barrier.

Use Epoxy Resin

This is a two-part resin that you mix together and then apply to your Styrofoam. It will seep into the foam and harden, creating a waterproof barrier. You can find epoxy resin at any hardware store.

The great thing about epoxy resin is that it can be used on any type of Styrofoam, including white Styrofoam. It is also clear, so it will not change the appearance of your foam.

To use epoxy resin, mix the two parts together and then brush it onto your Styrofoam. Make sure to cover the entire surface evenly. You can also use a spray bottle to apply the resin.

Let the epoxy resin harden for 24 hours before using your Styrofoam.

One downside of epoxy resin is that it is a bit more expensive than other options. It is also not as durable as some of the other options on this list.[1]

Use a Polyurethane Coating

You can waterproof your styrofoam by using a polyurethane coating. This type of material can prevent water from getting in. There are many different brands to choose from, so be sure to pick the best one for you!

If you want to make sure your styrofoam is fully waterproof, the first thing that needs doing is sanding it down. This will help the coatings stick to surfaces better, so they stay in place for longer!

Once you have completed one side of the project, you need to apply another thin layer of paint using either brushes or rollers. You should wait until the paint dries according to the label directions before applying the final finish. This will ensure that your project is as durable as possible.

Apply a lot of coating to your foam so that you get it into all the cracks and crevices. Use a brush or roller to apply an even layer of coating over the surface of your foam.

Allow the coating to dry completely before using your foam. This may take several hours or more, depending on the brand of coating you use.

Once the coating is dry, your foam will be waterproof and ready to use.

Polyurethane Resin

One-part polyurethane resin is easier to use, but it doesn’t have the same strength as two-part polyurethane resin. Two-part polyurethane resin is more difficult to use, but it will create a stronger waterproof barrier.

To use one-part polyurethane resin, simply brush it onto the styrofoam. To use two-part polyurethane resin, mix the two parts together according to the instructions on the package, then brush it onto the styrofoam.

Polyurethane Resin

Both types of polyurethane resin will take 24 hours to cure.

Once the polyurethane resin has cured, you can paint over it or leave it as is. If you’re going to be using the styrofoam outdoors, you may want to consider painting it a light color to reflect the sun’s rays and keep it cooler.

Use a Sealant

Applying a clear sealant is the most common method of waterproofing styrofoam. This can be in the form of a spray-on sealer, or a brush-on sealer. There are many types and brands of sealants available on the market. You will want to do some research to find the right type of sealant for your project.

Sealants provide a barrier that protects your home from both water and water vapor.Although sealants can help to protect styrofoam from water damage, they will not make it completely waterproof.

If you are using styrofoam in an area that will be constantly exposed to water, it is important to use a waterproofing agent in conjunction with the sealant.

Before you seal styrofoam, it is important to test the sealant on a small area.
This will help you make sure that the sealant doesn’t change the appearance of the styrofoam.

Can You Use Aerosols on Styrofoam?

Aerosols can be used on styrofoam, but they must be used sparingly and with caution. Aerosols can cause the styrofoam to expand and become brittle.

When you are spraying an aerosol, always test it in a place where no one will see first. You should apply light coats of paint, and make sure to let each coat dry completely before applying more. Applying more than one coat before the paint has dried can cause damage. Applying these sprays can cause the object to crack, so be careful not to press too hard.

There are a few different ways that you can waterproof your styrofoam. There are many types of sealers that you can use for your home. You can use a water-based sealer, a silicone sealer, or even just good old fashioned paint. Each method has its own set of advantages and disadvantages, so you need to do some research before deciding which one is right for you.

Making sure that you are well-ventilated when applying the coating will ensure a safe experience. This product gives off fumes that can be harmful if you breathe them in, so make sure to work in an open area with plenty of air flow.

Why Is My Styrofoam Hardening?

One common issue people have with styrofoam is that it begins to harden over time. This can be caused by a few different things, but the most likely reason is that the item has been exposed to air. Styrofoam releases water over time when it is exposed to air. This moisture causes the foam to swell and eventually harden.

Why Is My Styrofoam Hardening?

The best way to keep your styrofoam from absorbing moisture is by storing it in an airtight container and coating the material with sealant. This will create a barrier between you, preventing any water absorption.

If your styrofoam has already started to harden, there is unfortunately no way to reverse the process. However, you can try sanding it down or using a heat gun to reshape it.


What can I seal styrofoam with?

There are many types of waterproof barriers you can use on your foam. Each one has its own advantages and disadvantages, depending on what you want to achieve.

Polyurethane is a durable and flexible material that can be used in many different forms. One type of insulation, poly-urethane, does not have an odor like other substances do. It is easy to clean up with soap if it gets stained.

Silicone is a popular alternative to the traditional plastic based sealers because it will not yellow or crack over time when used on styrofoam.

Acrylic sealers will give your styrofoam a clear, glossy finish.

There are two types of silicone sealers: clear and white. Silicone can be used to create a watertight barrier on styrofoam. It will not yellow or crack over time.

If you are looking for a sealant for your floors, it is important to purchase one that is labeled as “waterproof.” Make sure you follow the manufacturer’s instructions on how long to wait before applying and drying completely. Failing to do so may cause damage or discomfort during use.

Sealing styrofoam is a simple process that only requires a few supplies. In addition to your chosen sealer, you will need a paintbrush, rags, and gloves.

Start by putting on your gloves. Open the container of sealer. Use the paintbrush to apply a thin layer of sealer to the styrofoam.

Work on small sections of the styrofoam. Seal it in one direction. Let it dry for the time recommended by the manufacturer.

After the styrofoam dries, you can apply a second coat of sealer. Once it dries, the styrofoam will be waterproof and protected from the elements.

Does Water Go Through Styrofoam?

It turns out that water can’t get through styrofoam after all! This is because the material doesn’t soak up water, so when it gets wet there’s no way for any of that moisture to get inside and damage it. This type of plastic is perfect for underwater sealants and insulation blankets. The plastic will not sink to the bottom and will stay in place.

How Do You Make Foam Waterproof?

There are different ways to make foam waterproof. You can use a spray-on product, or you can coat it with wax and apply an oily finish. This will keep water from getting through to the other side and causing any leaks.

When using a waterproofing spray on your foam, make sure that it is compatible with the material.

You need to apply the spray evenly over the surface of the foam. If you don’t, it will create an uneven surface which will be more likely to get water damage.

Once you’ve applied the waterproofing spray, you need to let it dry completely before you use the foam. If you don’t, the spray will simply rub off onto whatever you’re using the foam for.

Another way to waterproof your foam is to wax it. You can use any type of wax, but beeswax is a good option because it’s naturally water-resistant.

You need to melt the wax and then brush it onto the surface of the foam. Make sure that you spread it evenly across the surface.

Is all Styrofoam waterproof?

You can waterproof your styrofoam by using a spray-on coating. This will keep it dry for years to come. You could also seal the material with an expensive paint job that is guaranteed to protect it from moisture and fungus growth.

Waterproofing spray is a quick and easy way to make styrofoam water resistant. There are many brands of waterproofing spray available, so be sure to choose one that is compatible with styrofoam.

If you want to seal styrofoam, using a waterproof coating or paint is a better solution than just leaving it as it is. However, it will take more time and effort. Make sure to apply the coating evenly over the surface of the styrofoam using a brush or roller.

Useful Video: How to waterproof styrofoam and how to waterproof polystyrene for outside use


In general, most types of water will not penetrate styrofoam. However, if the styrofoam is submerged in salt water or seawater, it may start to disintegrate over time.

If you are looking for a way to waterproof your styrofoam, we recommend using a sealant like polyurethane foam. This will help keep out moisture and protect your styrofoam from any potential damage. Have you tried waterproofing your styrofoam? Let us know how it went in the comments!


  1. https://wigglywisdom.com/how-to-waterproof-styrofoam/