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Is expanding foam waterproof? Sundries

Is expanding foam waterproof?

Posted on 24 September, 2021

Expanding foam is a popular product that is also known as insulation foam. It has a variety of uses both in a domestic home setting and larger industrial environment and therefore it is bought by a large demographic of consumers.

The purpose of expanding foam is to fill gaps, prevent and block draughts, provide insulation to buildings and in some cases even dampen sound. What is more, once the foam has dried it can then be easily cut and shaved away. Paint can be applied if wanted and no one would even know that a gap had been plugged. As you can see the usefulness of expanding foam is high and hence why it is one of the most popular products on the market. However, how waterproof is it?

The answer is not a straightforward yes or no, as some foam requires damp conditions to work whereas others are unable to stick to a wet surface. It is for this reason that it is so important to properly research and prepare before using any expanding foam.

Where can I use expanding foams?

Firstly, consider where you are planning on putting the expanding foam. If you are trying to fill a gap on a window or door, then it is likely this foam will feel the effects of water damage more commonly. The same is true of any work that needs to be done in the kitchen or bathroom. Waterproof expanding foam is vital in these areas of the house. From a commercial or an industrial perspective, you may want the waterproof option for properties such as swimming pools or outdoor areas. One of the great benefits of expanding foams is that they can be used on a variety of surfaces such as concrete, brick, wood, plaster, plastic and metals.

Which ones are more waterproof?

Frustratingly, some expanding foams are waterproof. There are types of foams referred to as ‘open cell foam’. Open-cell foam is a product with a similar design as rubber which is made by mixing inflating agents with rubber. This gives off a gas that causes the foam to expand. It is known as open-cell due to half its cells being open. However, this form of expanding foam is not water-resistant or waterproof whereas closed-cell foams are. Also known as polyurethane foam, the cells are interlocked and this prevents any air or water from getting through. This makes it very water-resistant and a popular choice for rooms that are more likely to see dampness. It is important that you find out about the density of these foams, as low-density foams may not be waterproof although they can be water-resistant to an extent. Comparatively, higher density cell foams can be fully waterproof.

Polyurethane expanding foam is a strong candidate if you are searching for a waterproof expanding foam. This product is used in the building industry due to its strong waterproofing properties. Additionally, this can be an effective foam when seeking to plug leaks as the foam will expand into the gaps and bond with the surface.

How can I test it for myself?

The main thing you should do is properly research which types of expanding foam are waterproof. If you still have questions reach out to a professional and they will be able to give you a more detailed answer based on your specifications.

Our team here at BC Profiles is only an email away, so if you do have any concerns regarding using expanding foam in damp settings please let us know and we will do our best to give you an informed decision. If you still want to test out the foam yourself you can buy a few options and spray a hidden or little-seen damp area. You should be able to see very quickly which one has stuck the most effectively. This will be the foam that is the most water-resistant and waterproof.


As there are different types of expanding foams made by different chemical mixes, it is understandable that certain products would be waterproof whilst others wouldn’t.

BC Profiles has a large range of expanding foams, so once you have looked through our store and found the foam to suit your needs, feel free to ask us about any queries you have. 

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