Is Spray Foam Insulation Waterproof?

Technician spraying foam insulation

Spray foam insulation is a great product to use when it comes to insulating homes. It fills in all the cracks and crevices that could reduce the energy efficiency of your home.

It is a relatively easy to apply, inexpensive insulation solution that could complement other insulation methods you are using in your home.

However, an important question that often comes up is whether or not spray foam insulation can protect a home from water. The answer to this question is both yes and no.

Because there are mainly two types of spray foam insulation with different cellular structures and waterproofing capabilities.

These are open-cell and closed-cell foam insulation which behave entirely differently in regard to water intrusion.

Open-cell foam insulation has a more porous structure that allows water to pass through which is why not waterproof.

While closed-cell spray foam insulation is made up of smaller cells that are completely sealed in a more solid structure and are waterproof.

For the same reason, open open-cell spray foam insulation is a less expensive option because it can be used to patch up larger application surfaces with less material.

Closed-cell spray foam insulation is more expensive, but it provides a better seal and thus prevents water infiltration better.

What is a Spray Foam made of?

Spray foam is typically made of two components a polymer resin and an expansion agent typically isocyanate.

Spray foam is applied using a spray gun by mixing these two components at the tip of the nozzle to form an expanding foam. Once applied, it expands and fills gaps in the substrate to create an airtight seal.

The spray foam can expand up to 60 times its original size in liquid form. Thus, it can fill in any gaps or cracks offering a completely airtight seal.

Does open-cell spray foam insulation allow water through?

Yes, open-cell spray foam insulation does allow water to penetrate. Because it has a more porous cellular structure, water can easily pass through the insulation and reach the inside of your home.

Although open-cell foam insulation will provide an airtight seal around windows or other wet areas, it will not be waterproof.

This type of spray foam is often used for interior repairs and low-pressure applications such as filling cracks or gaps.

However, since it is not an organic material, it does not promote mold growth. When the insulation is dry, its effectiveness is unaffected. It simply provides a conduit for water and water vapor to go into and out of a specified location.

How much water can open-cell spray foam insulation absorb?

Open-cell spray foam can absorb anywhere from 5% to 70% of its weight in water. If you reside in an area where the humidity is continuously high, it is recommended that you use closed-cell spray foam to avoid water intrusion.

However, if you have already installed open-cell insulation and are having problems with moisture, you can coat the surface with a waterproofing agent to help remedy the situation.

Does closed-cell spray foam insulation allow water through?

No, closed-cell spray foam does not allow water to permeate. This is mainly because the cells in this insulation are completely sealed and form a tight seal with the substrate.

The material is also resistant to mold, mildew, and pests. However, the tight seal can also work against you in the event of a leak.

A leak coming off from a pipe or a water heater can go undetected for days under the insulation which may cause serious damage to your home.

You can watch the below video that shows how both open-cell and closed-cell foam insulation behave when water is poured on them.

How to waterproof open-cell spray foam?

Open-cell spray foam insulation can be waterproofed by using a coating material.

This will help to form a barrier on the surface of the insulation that will prevent water from infiltrating through the cellular structure.

You can use products like Xypex Concentrate which is a crystalline product that is mixed with water and applied to the surface of the open-cell spray foam insulation.

Alternatively, you can use a liquid membrane that will be sprayed on top of the insulation.

However, it is important to note that Xypex Concentrate and other waterproofing products will only cover the insulation.

Therefore, the treatment will only be effective as long as the coating remains intact, and the insulation is not damaged.

Should I use open-cell or closed-cell spray foam insulation?

The answer to this question really depends on your specific needs.

If you are looking for insulation that will prevent water infiltration, then closed-cell is the better option.

However, if you are more concerned about energy efficiency and reduced cost then open-cell would be a better choice.

PropertyOpen-Cell Spray Foam InsulationClosed-Cell Spray Foam Insulation
Cost-EfficiencyMore cost-effective than closed-cell foamMore expensive than open-cell foam
Insulation ValueR-value of 3.5-3.7 per inch of thicknessR-value of 6-7 per inch of thickness
Water ResistanceNot waterproof, can absorb water and retain moistureWaterproof, prevents water infiltration
SoundproofingOffers some sound insulation propertiesOffers better sound insulation properties
ApplicationEasier to install, can be sprayed quicklyMore difficult to install, requires professional application
DensityLess dense than closed-cell foamMore dense than open-cell foam
ExpansionExpands more when sprayed, can fill gaps more effectivelyExpands less when sprayed, may not fill gaps as well
Eco-friendlinessGenerally considered more eco-friendlyMay contain chemicals that are harmful to the environment
Comparison of Open-Cell and Closed-Cell Spray Foam Insulation

At the end of the day, it is important to understand that both forms have their unique benefits and disadvantages.

The choice really boils down to your specific needs in terms of cost-efficiency, effectiveness when exposed to water, ease of installation, etc.

Does spray foam insulation prevent mold growth?

Spray foam insulation has nothing to do with the growth of mold. Mold is a result of excessive moisture and high levels of humidity.

If you have an issue with mold, it is most likely because you do not have proper ventilation in your home.

If you spot mold in an area don’t apply any insulation until the issue is resolved. Since insulation reduces air circulation, it will only help to fuel mold growth.

If you notice mold growth on existing insulation, make sure to remove and replace the insulation immediately.

Does spray foam insulation cause condensation?

No, spray foam insulation does not cause condensation. Condensation occurs due to high levels of humidity and the temperature difference between adjacent surfaces.

For example, if the surface of your window is colder than the surface of the wall, condensation will form on the window.

If you are seeing moisture or water buildup in your home there may be another underlying cause, such as a leaky roof or faulty plumbing.

If you are not sure where the moisture is coming from, it is best to contact a professional to help diagnose and solve the problem.