Can You Put Spray Foam In A Kayak? [Why & Why Not?]

If you are trying to make sure that your kayak will stay on the surface if you capsize and you have heard of adding foam to keep it buoyant, you might be wondering whether spray foam is a suitable addition. We’re going to cover why it is and isn’t today.

Can You Put Spray Foam In A Kayak?

You shouldn’t use spray foam in a kayak. Because it won’t protect you in the event of a crash. In addition, spray foam is often open-cell meaning. It has a higher possibility of absorbing water than closed-cell foam. Therefore your kayak will take on water if it capsizes. There are also concerns with adding expanding foam to an enclosed cavity, as it could split the boat, even if one end is open.

Closed-Cell Vs. Open-Cell Spray Foam

Before we can get into why you shouldn’t use spray foam in a kayak, you first need to know the difference between the two types of spray foam.

Closed-cell polyurethane foam (SPF) consists of organic chemical compounds that are derived from petroleum extracts. This means it provides an air seal and continuous insulation. As a result, mildew and mold won’t form, unlike when using closed-cell foam.  

In addition, it is resistant to water absorption. 

Unlike open-cell spray is a rubber-like product that consists of inflating agents such as; sodium bicarbonate. The agents give off a gas that expands whenever the foam is exposed to water. 

We’ll discuss which type if any is best to use in a kayak below.

So, Why Do Some Kayaks Have Foam In them?

You have probably noticed that some kayaks contain foam inside the cockpit – and often, this foam seems a little cumbersome and gets in the way of your legs. However, according to FlatBottomBoatWorld, this foam serves a couple of important purposes.


The foam does not change where your kayak sits on the water when you’re climbing in and out of it; in fact, it adds a little weight, so if anything, it might make it sit slightly lower rather than higher.

The foam instead is useful when you capsize. 

If your kayak takes on a lot of water, it may sink, which can be disastrous in the wrong circumstances, sometimes resulting in the loss of the boat. It also means you have nothing safe to hang onto if you are in trouble.

The foam will help keep the kayak at or just below surface level, preventing it from sinking any further. This means you can recover the kayak or hold onto it in an emergency.


Secondly, this foam protects a kayaker’s legs in the event of a crash. It is usually found in whitewater kayaks, which are intended to take many knocks and bumps. And it helps the kayakers weather those knocks and bumps too.

If you hit a rock or other obstacle, you will jolt forward in the boat, and the foam provides a soft layer for you to hit. It protects your legs and knees from injury and will save you if the hull of the boat buckles inward.

So, the foam plays two important roles. It’s particularly useful for whitewater kayaking but can also be useful in calm water if you capsize. 

That means you might be looking at your kayak and wondering if you can add expanding foam to help it stay afloat.

This may seem like a cheaper alternative to other floatation options such as watertight bulkheads. Let’s look at whether it’s viable.

Why Might You Add Expandable Foam To A Kayak?

Expandable foam does seem an attractive option on the surface; you can fit it to the kayak’s shape easily (since it will expand itself into the cavity), and it is readily available and reasonably cheap.

It also seems like a good choice for floating; it is full of air because it is so porous, which means it’s reasonably light and seems like it should float well.

If you use other kinds of foam, you have to cut them to size, which can be tricky; they need to be fitted to the kayak’s inside, which often takes time and effort. Getting the right shape is not easy.

Many people opt to add expandable foam to their kayaks for this reason. They are particularly attracted by how light the product is. It may seem an ideal low-cost, low-work, low-weight alternative to purchasing and cutting other kinds of foam to size.

However, it isn’t a good idea.

Why Can’t You Put Spray Foam In A Kayak?

There are several different kinds of expandable foam, so you may be able to find one that does not run into this issue, but in general, expandable foam is open-cell and therefore absolutely not waterproof.

This totally defeats the point of using foam at all – and indeed, using an open-cell foam that soaks up water will actually make your kayak heavier. Therefore much more likely to sink if you accidentally capsize it. The foam will quickly absorb water and start pulling the boat down.

This fundamentally destroys the idea of using expandable foam to help a kayak float unless you can find a closed-cell expandable foam. Unfortunately, this is likely to be expensive and can run into other problems, which we will explore momentarily.

Its lack of waterproofing makes it unsuitable for general day-to-day use, even if the kayak is not capsized. In addition, the foam will inevitably get splashed and damp while you’re kayaking, and this will lead to moldiness over time.

If you decide to use spray foam, ensure you use closed-cell foam for those reasons. It is vital that every aspect of your kayak is waterproof and will not soak up moisture, or you will encounter issues with sinking and with molding even if you are careful!

Even without the waterproofing issue, expandable foam encounters other problems. One of the big ones is that it is hard to control and very easy to overfill a space with it. 

The expansion of this foam can be extremely powerful, and there are plenty of stories of people who have accidentally exploded the end of their kayaks by adding it.

You might think that adding it to an area that has an open end would safeguard you from this possibility. But, unfortunately, it does not. The foam can still expand with enough force to damage the kayak. And once it has begun to expand, there isn’t much that you can do to prevent this from happening.

Overall, these two issues alone are enough to deter most kayakers from adding spray foam to their kayaks. Add issues with messiness, difficulty in controlling where the spray foam ends up, and reduced storage space in the boat, and it is altogether an unappealing option for most people.

What Other Options Are There?

So, how else can you help to ensure that your kayak stays afloat? First, if you’re going to be whitewater rafting, it is recommended that you buy a kayak with the foam in place. As you will also need the other safety features, this foam is designed to maximize the protection for your legs.

However, if you’re just looking to ensure your kayak floats well if you capsize, there are a few things you can do that are low cost and simple solutions.

One of the popular and very low-cost (but perhaps not aesthetically pleasing options) involves adding pool noodles to the nose of the kayak. 

You may wish to secure these with elastic or other ties. But they should help keep the boat on the surface if it goes under.

Another solution is to buy closed-cell foam and fit it to the nose of the kayak. This may be time-consuming, but it will work and won’t destroy your kayak in the process.

Where to Buy Closed Cell Spray Foam?

As mentioned above, it’s harder and more expensive to buy closed cell spray foam. Yu will be able to find some for sale on Amazon, Home Depot, Lowes, and some other retail sites. 

Make sure that it clearly states the foal insulation sealant is closed-cell. If it doesn’t say closed-cell, it’s likely open-cell. Another way to tell if it’s closed-cell is to check the price. The closed-cell foam will be more expensive. 

Final Word

Spray foam is not a suitable addition for a kayak. It is not waterproof, so it will not keep your kayak afloat, and it may mold after use on the water. Instead, choose a closed-cell foam or other floatation methods if you’re concerned about your kayak sinking.

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