Is expanding foam waterproof?

Author: Marshall McLaughlin  |  Last update: Tuesday, July 15, 2025

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.

Can expanding foam be used for waterproofing?

Expanding foam insulation is known for keeping water out very well. It's perfect for sealing buildings from water damage. Since it makes a tight seal, it protects from moisture problems. This kind of insulation is great for keeping a building safe and dry.

What happens to expanding foam if it gets wet?

To answer your question, yes foam does lose its insulation value when it gets wet, but not 100% of it. And no, it will not dry out.

Is Great Stuff expanding foam waterproof?

Flexible and easy to apply, GREAT STUFF™ Window & Door Insulating Foam Sealant quickly and cleanly forms airtight, water-resistant seals between framework and rough openings that withstand the elements.

Is gorilla expanding foam waterproof?

Product information

This 750ml expanding foam filler by Gorilla Filler is perfect for weatherproofing and sealing gaps. It expands to fill voids, providing an airtight and waterproof seal.

Expanding polyurethane canned spray foam test in WET CONDITIONS. Lifeboat Conversion Ep46 [4K]

Which expanding foams are waterproof?

Soudal Expanding Foam Gun Grade 750ml. Soudal is a name you can trust when it comes to waterproof expanding foam, and our Soudal expanding foam gun grade 750 mm can is no exception.

Where not to use expanding foam?

While it is hugely useful, it should not be used to solve all problems. One such example is electrical boxes. Expanding foam shouldn't be used in these locations as it could cause jams that would be expensive to repair. So avoid using it around sockets or light fixtures, or any electrical components in the property.

Can water get through spray foam?

Closed cell spray foam, in particular, is often touted for its ability to resist water and even act as a vapor barrier in certain applications. On the other hand, open cell spray foam and RetroFoam insulation are more permeable, which means they allow water vapor to pass through but still do not retain liquid water.

Will expanding foam set in the rain?

However, this form of expanding foam is not water-resistant or waterproof whereas closed-cell foams are.

When should you not use great stuff foam?

Not for use in aviation, or food/beverage contact, or as structural support in marine applications. 8. Do not use GREAT STUFF™ Insulating Foam Sealants for filling closed cavities or voids such as behind walls and under tub surrounds.

Will expanding foam stop a water leak?

To answer shortly: YES, spray foam can resist water from entering your home. The air-tight sealing it provides helps keep moisture from seeping inside and damaging your property. Many use it successfully for sealing home spaces prone to leaking, including crawlspaces and basements.

What destroys expanding foam?

Yes, WD-40 does remove expanding foam as it can break down the foam residue.

How long does expanding foam last?

On average, fire rated expanding foam can last anywhere from 10 to 20 years, depending on the conditions mentioned earlier. Fireproof expanding foam that is well-maintained and installed correctly in a stable environment will typically last longer.

Is there a spray foam that is waterproof?

Fortunately, closed-cell spray foam is waterproof. This makes it easier to rely on for controlled insulation no matter where your home may be or what the conditions outside are.

Can water penetrate expanding foam?

Closed-cell spray foam insulation is highly moisture-resistant, meaning it can handle some level of wetness without immediate damage. However, it is not completely waterproof and prolonged exposure to water may eventually degrade its properties.

Does spray foam create a watertight seal?

Closed-cell spray foam provides an impermeable moisture barrier which qualifies it as a waterproof material. This type of foam is denser, with a closed-cell structure that creates a strong, rigid layer that water cannot penetrate.

What happens to foam when it gets wet?

Homes with open cell spray foam don't have to replace the foam when it gets wet, or even after it has been submerged. This might come as a surprise because there is a common misconception that all open cell spray foams absorb water like a sponge and retain it, but that's not the case.

What foam is used for waterproofing?

Bostik Expanda Foam. Bostik Expanda Foam is a one component, multi purpose polyurethane foam with powerful adhesive qualities that expands to fill gaps of all dimensions. It will not shrink and cures to an airtight, moisture resistant seal.

Is gap filling foam waterproof?

Don't use expanding foam as a permanent solution to leaks

The expanding foam will fill the gap however should you not fix the initial water damage, the leak could move into other parts of the basement. Furthermore, the expanding foam isn't completely waterproof and therefore over time it could break down.

Can mold grow under spray foam?

Mold and mildew can begin growing behind the insulation which can go unnoticed until it's already become a huge problem. This often happens when the spray foam isn't installed correctly and space is left between the insulation and the wall, which allows moisture in and gives mold the perfect place to grow, unfettered.

Can you fix a roof leak with expanding foam?

It is particularly beneficial in roofing projects, where it is used to seal gaps and prevent water leaks.

Does rain affect spray foam?

Weather and Spray Foam

Besides the temperature changes that come with winter weather, other weather effects such as rain can also stall a spray foam insulation job. You want to make sure the surface you're spraying doesn't contain excess moisture, or you could have adhesion problems.

What is the downside of using expanding foam?

While spray foam insulation can make a home more energy efficient, its downsides often out-weight its benefits. If spray foam insulation isn't installed correctly or is used in the wrong setting, it can cause all sorts of problems, from reducing ventilation to rotting wooden roof beams.

What kills expanding foam?

Solvents like acetone and WD-40 are the fastest way to dissolve hardened expanding foam.

When should you not use spray foam?

Directly against electrical wiring or fixtures: Spray foam insulation should not be applied directly against electrical wiring, fixtures, or recessed lighting unless they are rated for contact with insulation. Contact with insulation can cause overheating and pose a fire hazard.

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