Narrowboat Spray Foam Insulation
Specialist narrowboat spray foam insulation for steel hulls — closed-cell Enverge foam controls condensation, eliminates hull sweating and protects liveaboard, hire-fleet and trip-boat craft against the cold steel of the waterline.
Why spray foam for narrowboats
Steel narrowboats live half-submerged in cold water, which makes the entire hull a permanent cold bridge. Warm, moisture-laden cabin air — from cooking, the stove, washing and simply breathing — meets that cold steel and condenses, soaking battens, ply linings and ballast. Closed-cell spray foam is the marine solution because it raises the steel's internal surface temperature and forms an unbroken thermal and moisture barrier across the hull.
Unlike loose batt or board insulation stuffed behind linings, our Enverge closed-cell foam self-bonds to the steel as it cures, expanding into every rib, stringer and awkward cabin-side curve with no gaps, no fixings and no air paths for moist air to track behind. The result is a seamless monolithic layer that follows the exact geometry of the hull — the only way to reliably defeat hull sweating on a curved steel craft.
Whether the boat is a private liveaboard, a hire-fleet cruiser or a passenger trip boat, the insulation is fitted at fit-out stage or during a re-fit before linings go back on. ThermoFoam works to the boat builder's or operator's programme, coordinating with the joinery so the foam is trimmed clean and ready for battens, ply and final cabin finishes.
The benefits for narrowboats
Stops Hull Sweating
Raises the internal steel surface above dew point so cabin moisture no longer condenses and runs down the hull sides.
Stove Heat Stays In
Closed-cell foam holds the multi-fuel stove's warmth in the cabin instead of bleeding it into cold steel and canal water.
Self-Bonds To Steel
Sprayed foam adheres directly to the hull as it cures — no battens, fixings or trapped air gaps behind the lining.
Seamless Over Curves
Expands into ribs, gunwales and cabin-side curves as one continuous layer, sealing the awkward geometry batts can't follow.
Protects Ply & Battens
A dry hull means linings, ballast and timber framing stay sound, cutting rot, mould and costly re-fits over the boat's life.
Hire-Fleet Ready
Durable, low-maintenance insulation suited to hard-worked liveaboard, hire and trip craft that sit on the cut year-round.
Engineered For Steel Hulls
A narrowboat hull is a continuous cold steel surface sitting in cold canal water, so every internal void becomes a dew-point trap. Our closed-cell Enverge system self-bonds directly to the cabin sides, baseplate and gunwales, lifting the inner surface temperature above dew point and shutting out the condensation that rots ply linings and bilges.
Enverge closed-cell foam is sprayed directly onto prepared, de-rusted steel where it expands and self-bonds to form a rigid, low-permeability layer across the hull. By lifting the internal steel surface temperature above the cabin dew point, it removes the cold surface on which condensation forms — controlling hull sweating without battens, fabric or mechanical fixings.
- Self-bonds to the steel hull — no battens or fixings
- Seamless over ribs, gunwales and cabin-side curves
- Controls condensation and hull sweating at source
- 25-year manufacturer-backed product warranty
Enverge Nexseal LE — verified performance
Typical published values for Enverge Nexseal LE closed-cell foam. Full technical specification →
Specification & compliance for narrowboats
Steel hulls sweat: warm cabin air meets cold plate and condenses, corroding the vessel from the inside and soaking fit-outs. Closed-cell foam sprayed at 25–75 mm bonds directly to the hull and deckhead, following every curve, rivet and weld — surfaces rigid boards simply can't follow — and carries its own vapour barrier, so no separate membrane is needed.
Most narrowboats, widebeams and workboats are completed in one to two days. The foam adds rigidity, keeps condensation off the steel permanently, and is backed by a 25-year manufacturer product warranty.
From enquiry to warranty
Enquire
Tell us about your narrowboats & building.
Survey
Free survey of your narrowboats & condensation check.
Specify
The right system for your narrowboats.
Install
Approved applicators, minimal disruption.
Warranty
Handover pack & 25-year warranty.
Real narrowboats spray foam applications
Commercial projects
University Hospital of Wales
Low-odour, fully documented install in a live healthcare site.
Derriford District Centre
Spray foam insulation for a busy public-sector building.
Newport Leisure Centre
Pool-hall insulation controlling humidity and heat loss.
Get a quote for your project
Send us your building details and our technical team will specify the right system and a clear budget. No obligation.
Narrowboat insulation, answered
Why is spray foam used on narrowboats instead of batt insulation?
A steel hull is curved and ribbed, and any air gap behind batt or board lets moist cabin air reach the cold steel and condense. Closed-cell spray foam self-bonds to the hull as one seamless layer, following the geometry exactly and leaving no path for hull sweating.
Will spray foam stop condensation inside the cabin?
It controls the main cause. By raising the internal steel surface temperature above dew point, the foam removes the cold surface that condensation forms on. Combined with sensible cabin ventilation, this keeps linings, ballast and timber dry through year-round use.
Can you insulate a boat that's already fitted out?
Best results come at fit-out or during a re-fit, when linings are off and the bare hull is accessible. We coordinate with the boat builder or joiner so foam is sprayed onto clean steel, then trimmed ready for battens, ply and final cabin finishes.
Is the foam suitable for hire fleets and trip boats?
Yes. Closed-cell foam is rigid, durable and low-maintenance, which suits hard-worked hire-fleet and passenger craft that sit on the water all year. It keeps cabins warmer, stove heat in, and protects the hull lining between charters and seasons.
Does the foam carry any certification or warranty?
The Enverge closed-cell system (Nexseal LE) is supplied with Duratite as UK distributor of record. It carries a 25-year manufacturer-backed product warranty — never insurance-backed — giving operators long-term assurance on the installed system.
How long does boat insulation take?
Most vessels are sprayed in 1–2 days depending on size and access — far faster than batten-and-board methods.
Will it stop hull condensation completely?
Yes — closed-cell foam seals the steel so warm cabin air never reaches a cold surface, stopping the sweating that drives corrosion.
What depth is applied to a hull?
Typically 25–75 mm depending on the vessel and how it's used — specified after survey.
Insulate your narrowboats the right way
Specialist commercial spray foam, installed UK-wide by the Duratite Group's spray foam specialists.
Book a Free Survey →or call 01208 832 602