Narrow boat insulation is used not just for keeping warm in the winter but also for keeping cool in the summer and for reducing condensation from habitation. The main type of insulation found on narrowboats is polyurethane (PU) foam. The Fit Out Pontoon offer nationwide PU sprayfoam services for narrowboats and widebeam canal boats.

Narrowboat spray foam insulation
Spray on polyurethane (PU) foam is a popular choice for insulation on a narrow boat
Narrowboat insulation applied during the fit out of a new narrow boat

Insulation… Polyurethane (PU) Foam

By far and away the best option for insulation on a narrow boat is spray on polyurethane (PU) foam. It is closed cell, so is impervious to moisture penetration. There is no air gap between the insulation and the steel skin because it bonds to the steel.

No air gap (thermal break) means no condensation. Where there is the possibility of a thermal break, for example if a bearer has been stripped of its layer of insulation in order to provide an even surface, the break can be bridged with metallised foil insulation or bagged insulation under the timber sheet panel.

Because PU foam insulation is spray applied, it can be laid on as thick or thin as necessary, so bearers can be coated as well as flat panels. It can also be sprayed over timber batons, adding strength and moisture resistance to the structure. As well as a thermal insulator, it can also reduce vibration and noise carried by the hull.

A sailaway narrowboat / widebeam will usually come insulated, even a basic sailaway. It is only if you are buying a basic hull only that you would need to consider our PU sprayfoam insulation services. However, if you are fully re-fitting an older narrowboat or widebeam canal boat, you may find you need to replace the existing insulation.

If you would are considering our sprayfoaming services, below are our price per foot charges:

£40.00 +vat per foot for narrowboats up to 6ft 10″ wide

£45.00+vat per foot for widebeams up to 10ft wide

£50.00 +vat per foot for widebeams up to 12ft 6″ wide

Please note these prices include travel up to a 50 miles radius of Nottingham

If you would like any other items spray foaming such as house boats or containers please free to get in touch.

Insulation… Expanded Polystyrene

Early narrow boats for leisure were insulated by big sheets of expanded polystyrene. This material is still used today by some converters and it has its place in terms of cost and ease of use. There are potential issues though.

PVC Wiring

PVC wiring reacts with polystyrene insulation. Polystyrene causes plasticisers used in the manufacture of older cabling to migrate thus causing the insulation to go brittle. The potential issue is where there is direct contact of the styrene and PVC sheath close to metal parts that may cause a short circuit if the cable breaks or the insulation cracks. Boat builders are aware of this now and so will run services via conduit if they are using styrene sheet.

If you are the owner of an older narrowboat it may be worth checking the integrity of the wiring where it is in contact with polystyrene sheeting. It is good to know that there is polystyrene resistant cabling available for repairs and upgrades. Polystyrene sheets must also be fire retardant.


The other issue is efficiency. It is impossible to completely cover the steel shell with sheets of polystyrene. The sheets have to be meticulously sealed to form a vapour barrier and this barrier can be breached over time. When this happens warm air from the interior gets around the polystyrene sheeting and condenses on the cold steel of the outer shell. This condensation can be considerable. It is not beyond the realms of possibility that over 10L of water could be produced in a very cold month. The only place this condensation can go is into the bilges. Many owners just don’t know it’s there. Come spring and summer, the bilges dry out and there is no issue. However, over time this wetting and drying will cause corrosion. The last place an owner needs corrosion is in a cabin bilge where it is often impossible to see. We would highly recommend making an access hole into the cabin bilge at the rear of the narrowboat so any build up of condensation can be removed as soon as possible.

The above also applies to rigid polyurethane sheet and polyisocyanurate rigid sheet.


Not what you're looking for? Try some other items within this chapter...

crick boat show 2024

(Saturday 25 to Monday 27 May 2024)


Britain's biggest inland waterways show.

Advance tickets can be ordered by phone and online until 12midday on Friday 17 May 2024. If you are planning to purchase advance tickets, we recommend that you do so well before this deadline to allow time for postal delivery.
Children 16 and under – free entry Saturday, Sunday, Monday

Trade & Preview Day – Friday 24 May 2024
Get ahead and visit The Fit Out Pontoon before everyone else on Preview Day!
Preview Day tickets are strictly limited to a maximum of 1,000 pre-booked visitors and give entry to the Show from 10am – 6pm on Friday 24 May.