The Best Expanding Foam For All Jobs

Expanding foam is an incredibly versatile part of any builder’s toolkit. Great for filling, sealing and insulation, these foams have uses across a wide range of construction and DIY tasks.

As anyone who has tried cleaning expanding foam will attest, using it correctly is something that takes skill and patience. It’s also important to know that not all expanding foams are the same, and some are much more suited to certain tasks than others.

What to Look for in Expanding Foam

If you don’t use expanding foam often, you might assume that they’re all kind of similar. However, if you want to do good work, it’s crucial to know what features define certain foams against other choices.

The most robust and versatile form is known as one-part polyurethane (or PU) foam. This is the standard expanding foam sold in 750ml cans, either with its own applicator or to be fitted into a standard expanding foam gun. If you’re looking to fill a large gap, this is probably what you’ll want.

However, certain expanding foams come with unique properties, chemicals and features that make them particularly suited for certain jobs. Alternative features of expanding foam include:

• High- and low-density foams: Low-density foams expand much more but are slightly pliable once set, which can be good for insulation but offers no load-bearing strength.
• Open- and closed-cell foams: Similar to high- and low-density foams, open-cell foams expand much more, while closed-cell foams form a more solid, waterproof barrier, crucial for outdoor use.
• Fire foam: Any foam designed to offer a level of fire protection. Fire-stop foams usually work by expanding and hardening when in contact with fire, slowing its movement through a building.
• Latex foam: An alternative foam that expands much less than traditional PU foam, suitable for small cracks and gaps. Also water-based, so easier to clean if applied incorrectly.

As you can probably guess, understanding what features make for the best foam comes down to the application. Here is a rundown of some of the most popular uses for expanding foam and the features or products we’d recommend you consider.

The Best Expanding Foam for Insulation

The best expanding foam for insulation does not include spray foam insulation, where a PU foam is applied over a large area to provide an alternative to traditional insulation rolls or boards. That is a job for a dedicated spray insulation professional.

However, even when installing traditional insulation, expanding foams can still play a role.

If working with insulation panels, it is common to use a fixing foam adhesive. This is a polyurethane foam with less expansion but more adhesion, providing a firm grip on materials before setting. Fixing foams are usually suitable for both horizontal and vertical applications, helping to ensure insulation boards are secure and in place.

If you’re installing insulation in a stud wall and need expanding foam to close gaps, then you may want to consider foams with soundproofing qualities. Open-cell foams – sometimes marketed as acoustic foams – are less solid and are better for trapping things like sound and heat (although they are obviously not enough on their own for complete soundproofing).

The Best Expanding Foam for Outside Use

The most important thing to consider when using expanding foam on outdoor projects is, of course, waterproofing. Thankfully, most PU expanding foams are closed-cell, which provides a good waterproof barrier.

To help protect the foam throughout its life, it’ll also need UV protection, otherwise it can degrade over time. Some expanding foams specifically designed for outdoor use may have this built in, but if not, you can usually apply a coating to a regular expanding foam once it has cured.

The Best Expanding Foam for Plasterboard

When choosing expanding foam for plasterboard, you have the same considerations as with insulation.

If using expanding foam to help secure plasterboard, then an expanding foam adhesive is what you’ll want to use. These foams are specifically designed to create a secure, long-term hold.

If looking for expanding foam to fill gaps around a plasterboard wall, then you may want to consider features such as insulation and soundproofing. You may also need to consider a specialist fire stop foam, which not only offers both those features but also includes a degree of fire protection.

The Best Expanding Foam for Small Gaps

Whenever looking to fill small gaps, it’s worth considering a high-density, low-expansion foam. These are sometimes called precision foams or window and door foams, and are designed to expand much less than a traditional PU foam.

Depending on the project, you may also want to consider a latex foam. Similar to low-expansion PU foams, latex foam expands much less than a traditional product. It is also water-based, easier to clean and less toxic, so it may be a good choice if you’ve not worked with expanding foam much in the past.

The Best Expanding Foam for Windows

Whenever working with windows or doors, it’s important to use a low-expansion, high-density foam as discussed above.

A regular foam can expand aggressively many times beyond its original size, which can potentially cause windows to bow and buckle if not applied correctly. A low-expansion foam is usually applied with a smaller nozzle and expands much less, helping to protect your frame.

When using expanding foam on windows, you also need to consider things like water, heat and UV resistance. High-density foams are usually good for all of these, and because they set hard, they can be sanded and coated with other products to get the right level of protection.

No matter your project, our range of building products, including expanding foams, will ensure you have everything you need to get the job done. We also stock expanding foam guns and gun foam cleaners, which can make life much easier for those using these foams regularly.