As we move into the Autumn months, insulating your narrowboat should become a top priority. By having properly installed insulation, you will be able to keep warm without using too much energy during the colder months.

With that in mind, we’ve narrowed down the best insulation options for your narrowboat and explained how you can install them. 

Spray Polyurethane Foam

This is widely regarded as the best option when it comes to narrowboat insulation. Because this type of insulation is applied using a spray, it can be laid on as thick or thin as you want.

The main selling point of spray polyurethane foam is its versatility. It can be applied to just about anywhere, whether you want to insulate your floors, internal walls or ceilings. Furthermore, in addition to being a great thermal insulator, this type of foam is also a sound insulating product, meaning you can use it to reduce noise and vibrations such as those given off by your engine.

Another advantage of spray polyurethane foam is its ease of use. It can be applied very quickly and is easier to install than rock wool and sheet insulation.

It’s also much better at keeping heat in the narrowboat, so you can have a thinner layer than you would with rock wool.

How to apply this solution:

Shake the can of foam strongly for 30 seconds so that the foam is a suitable temperature. Then, turn the can upside down and fix it to the spray gun.

Next, remove the dirt, dust and grease from the surface you want to apply the foam to and moisten it with water. Finally, turn the can upside down and press the trigger of your spray gun.

This foam needs to be sprayed directly onto the inside of the hull. Once it’s been applied, it will start to expand.

This video shows spray polyurethane foam in action and visualises the above steps…


Rock wool

Another great insulation option is rock wool.. This is a high-density material with a non-directional fibre orientation. What this means in simple terms is that it not only delivers high thermal insulation performance, it also reduces sound vibrations in your narrowboat.

It’s easy to cut, shape and fit too – even in awkward spaces. You can fit rock wool around cables, pipes and sockets with minimal difficulty. Unlike spray polyurethane foam, there’s no need to protect wiring from this type of insulation.

Rock wool is also ideal from a safety perspective. Good quality rock wool can withstand temperatures of up to 1,177°C, is non-combustible and carries the highest Euroclass A1 fire rating. Therefore, it’s an effective form of fire protection.

The only downside to using rock wool is you’ll have to measure the interior of your narrowboat thoroughly to figure out much material you’ll need. However, because it’s so easy to fit and leaves no gaps in your insulation, it’s well worth the extra effort. It’s also very good at preventing water vapour build-up, which helps prevent mould.

How to apply this solution:

It’s important to take the necessary safety precautions when installing rock wool. This means wearing a dust mask, gloves and long sleeves to avoid itching.

To apply rock wool, simply take your batt and push it into your narrowboat’s cavities. Start at the top and use your hands to work it into the rest of the cavity so that it stays in place.

You should start with the cavities that don’t have any cables or pipes in them, as the rock wool is easy to install here. When it comes to the cavities which contain wiring or pipes, you need to cut the rock wool so that it fits around them, rather than pushing against them.

The below video explains these steps in more detail...



Once the most common form of insulation for narrowboats, polystyrene isn’t used as often today. That said, it still has its place in the boating world.

It provides excellent thermal insulation across a range of applications such as walls, roofing, refrigerators and freezers. Unlike other insulating materials, it’s water resistant and can protect your narrowboat against rain, snow, ice and hail. What’s more, it’s durable and built to last, which is a bonus if you’re looking for a long-term solution.

Another important benefit of polystyrene insulation – which it shares with the other solutions in this article – is that it’s easy to install. However, it can’t be used to insulate the entire narrowboat, so you will need to use a sealant as well.

Not only that, it can go brittle if it’s in direct contact with PVC wiring, which can lead to a short circuit. Therefore, if you use this form of insulation, make sure that you get it serviced to stop this from becoming an issue.

How to apply this solution:

The tools you’ll need to apply polystyrene insulation are a hammer, nails, brackets, knife, tape measure, safety glasses and safety gloves.

To apply polystyrene insulation, cut the material down to the size and shape of the area you wish to insulate. After this, place it in the area and check it sits neatly.

Once that’s confirmed, take it back out and nail the brackets to the joists for the polystyrene to sit on. This will prevent it from slipping out of place. Make sure not to place the joists too close to their edge – you want the polystyrene to sit flush with it.

When all six brackets are nailed in and positioned equally around the area, place your polystyrene on top. Push it down around all the edges to make sure it sits snugly in place. Repeat this for each panel you wish to insulate.

Check out this video if you want more information on how to install polystyrene insulation…


Narrowboat insurance from Insure4Boats

While having strong insulation in your narrowboat is important, having the right insurance is even more vital. Without it, you will not be covered against any accidental damage you cause to your own narrowboat or even other people’s.

With Insure4Boats, you can get the protection you need with our specialist narrowboat insurance. Simply complete a quote online within a few minutes and you will have all the protection you need.