Do Aluminum Boats Need Foam | Answered

Boat owners quite often wonder if they need to have foam insulation installed in their boats. In order to answer this frequent question, we need to look at how aluminum boat building is regulated by the Coast Guard.

The Code of Federal Regulations (CFR) establishes any vessel with a hull construction under 20 feet needs to have foam floatation in the boat.

There are a few reasons why foam floatation is used in boats. Foam is a very dense material, which means that it can provide a lot of buoyancy for its weight. Additionally, it is a closed-cell material, which means that the air bubbles within the foam will not escape. This makes the foam very effective at providing flotation.

Foams are added in aluminum boats to add buoyancy to the hull, and also to allow a boat that has a lot of holes or openings in its hull, such as a boat that has been damaged by corrosion or is used for fishing, to remain afloat. It acts as a safety barrier in these instances.

What Kind of Foam Do You Use in The Aluminum Boat?

There are a few different types of foam floatation that are used in aluminum boats. The most common type is polystyrene foam, which is a lightweight, closed-cell foam. This type of foam is often used in insulation and construction projects.

Polyurethane foam is another type of foam that is often used in boat construction. This type of foam is denser than polystyrene foam and is effective at resisting water absorption. Lastly, there is Expanded Polystyrene (EPS), which is a lightweight, open-cell foam.

EPS is not as effective as polyurethane or polystyrene foams at resisting water absorption, but it is more cost-effective.

Polyurethane foam is often used in aluminum boats because it is denser than polystyrene foam, and therefore provides more buoyancy. Additionally, it is effective at resisting water absorption, which makes it a good choice for boats that will be in contact with water.

Adding foam in boats can have several advantages and disadvantages. One advantage is that it can add insulation and help keep the boat warmer in cold weather. This can be important for fishermen since colder temperatures can make it harder to fish. Another advantage is that foam can help make the boat more buoyant, which can be helpful if the boat begins to take on water.

However, adding foam can also have some disadvantages. One disadvantage is that it can add weight to the boat, which can make it harder to move and use. Additionally, adding foam can increase the cost of manufacturing the boat.

Another disadvantage is if the foam absorbs water over a period of time. If this happens, the foam can become very heavy and un-buoyant. This can make it more difficult to use the boat, but also dangerous since it could sink if there is enough water in the foam.

Things to Consider Before Putting Foam in Aluminum Boats

If, you are putting foam in your aluminum boat make you inspect the hull properly for any leaks or corrosion. Once you have dealt with that applying an epoxy resin coat before applying the foam will ensure that the aluminum does not oxidize and the foam does not get wet.

First, fill the void with foam before you lay the decking. You can either block out the area for the drain-way while you pour, or you can pour the foam solid and then cut it and remove it after it has set.

How Much Foam Is Needed to Float an Aluminum Boat?

The answer to this question is how much floatation you need for your boat. Your answer will depend on the structural and material changes of the boat. Aluminum boats typically use Polyurethane foam, insulation to add buoyancy. This foam is available in different densities and thicknesses and you’ll need to match your original flotation or get close.

Check with your shop or manual how many pounds of foam you need per cubic feet of your boat and then you can estimate the amount of Polyurethane foam you need.

How Do I Know if My Boat Foam Is Waterlogged?

There are several methods of knowing if your boat foam is waterlogged. The easiest is placing a moisture meter on the boat and noting the readings at different places on the boat. This should give you a fair idea of the flotation value of the boat foam.

Next, if you have access to the underneath of your aluminum boat you can check if the boat is waterlogged by looking for rust stains on areas of the aluminum where water has lain against it. This may be difficult to find with fiberglass boats but is basically a “pull-up” test since you only need to lift up the corner of the boat and see if there are any layers of brown algae.

The last way of knowing if the foam in your boat has absorbed moisture is by checking that there are no signs of mold or mildew underneath the boat’s decking. Once you notice any of these signs it is time to remove the foam and place new, dry foam in the hull.

How Do You Dry Foam on A Boat?

The best-known way to dry out a waterlogged foam is simply by making the boat sit in sun for a few days. This should dry the foam out after which you can replace it with new foam. If you don’t have access to direct sunlight, placing heat lamps underneath the boat will also help to dry up the insulation material.

Make sure to inspect properly for holes if your foam is waterlogged. Make sure to work on the holes or cracks first before you plan to completely re-do with the foam.


The foam you use in aluminum boats will depend on the type of boat and what you want to do with it. Polyurethane is a good choice for most purposes, but if your goal is just buoyancy then polystyrene may be enough. When considering how much foam you need, remember that there are several different types of foams available with varying densities and thicknesses that offer differing levels of insulation or buoyancy depending on your needs. But to sum this up you will always need to add foams to your aluminum boats if they are under 20 Ft.