Open cell and closed cell spray foam are two fundamentally different insulation systems. Choosing the right one depends on the application, the substrate, the environment and the performance requirements. This guide explains the differences using UK building standards, UK products and UK pricing.
What Is Open Cell Spray Foam?
Open cell spray foam (such as Enverge Sucraseal) has a soft, sponge-like structure where the cells are not completely closed. Air fills the open cells, giving the foam its insulating properties. It expands significantly during application (up to 100x its liquid volume), making it excellent for filling large cavities quickly.
- Thermal conductivity: 0.035–0.038 W/mK
- Density: 8–12 kg/m³
- Vapour permeability: allows moisture to pass through (breathable)
- Sound absorption: excellent acoustic performance
- Typical applications: stud walls, timber frame, internal partitions
What Is Closed Cell Spray Foam?
Closed cell spray foam (such as Enverge Nexseal LE) has a rigid, dense structure where every cell is completely sealed. This creates an integral vapour barrier and gives the foam exceptional structural strength.
- Thermal conductivity: 0.027 W/mK (lowest in the UK market)
- Density: 30–35 kg/m³
- Vapour permeability: acts as its own vapour barrier
- Typical applications: soffits, hangars, containers, boats, piling, corrugated roofs
Head-to-Head Comparison
| Feature | Open Cell (Sucraseal) | Closed Cell (Nexseal LE) |
|---|---|---|
| Thermal conductivity | 0.035–0.038 W/mK | 0.027 W/mK |
| Thickness for 0.25 U-value | ~90–100mm | ~50–55mm |
| Vapour barrier | No (breathable) | Yes (integral) |
| Structural strength | Soft, flexible | Rigid, load-bearing |
| Water resistance | Absorbs moisture | Resists moisture |
| Acoustic performance | Excellent | Good |
| Cost per m² installed | Lower | Higher |
| Declared performance standard | BS EN 14315-1 | BS EN 14315-1 |
| Fire rating with DC315 | Class 1 | Euroclass B-s2-d0 |
When to Use Open Cell in the UK
Stud wall insulation — filling timber or steel frame cavities. Internal partitions — where sound insulation is primary. Timber frame new builds — where a separate VCL is specified. Budget-sensitive projects — where vapour barrier is not required.
When to Use Closed Cell in the UK
Below-ground applications — piling, basements, retaining walls. Marine insulation — narrowboats, vessels. Metal buildings — hangars, quonset huts, corrugated roofs, containers. Swimming pools — high humidity environments. Soffits — where Euroclass B fire rating is required.
UK Building Regulations: Part L
| Element | New Build | Retrofit |
|---|---|---|
| Walls | 0.18 W/m²K | 0.30 W/m²K |
| Floors | 0.13 W/m²K | 0.25 W/m²K |
| Roofs | 0.13 W/m²K | 0.16 W/m²K |
| Soffits | 0.18 W/m²K | 0.25 W/m²K |
Nexseal LE needs ~50–80mm. Sucraseal needs ~90–150mm. This is why closed cell is preferred where space is limited.
Cost Comparison UK
| Open Cell | Closed Cell | |
|---|---|---|
| Installed cost per m² | £8–£15 | £15–£30 |
| Thickness needed | 90–150mm | 50–80mm |
| Separate VCL needed? | Often yes | No |
| Total system cost | Similar when VCL included | All-in-one |
Free quotations for both systems. Call 01208 832602.
Duratite Products
Sucraseal (Open Cell) — Enverge. 0.037 W/mK. Performance declared to BS EN 14315-1. Breathable. Ideal for stud walls, timber frame, acoustic partitions.
Nexseal LE (Closed Cell) — Enverge. 0.027 W/mK. Performance declared to BS EN 14315-1, backed by a 25-year manufacturer product warranty. Integral vapour barrier. Low exothermic. Ideal for soffits, hangars, boats, containers, piling, pools, corrugated roofs.
Both installed by Duratite’s nationwide approved installer network.
Frequently Asked Questions
Can you mix open cell and closed cell on the same project?
Yes. Many projects use both — closed cell on external walls/roof, open cell on internal partitions for acoustics.
Is closed cell worth the extra cost?
For any application requiring a vapour barrier, moisture resistance or maximum performance in minimum thickness — closed cell is the only appropriate choice.
Which is better for soundproofing?
Open cell. The soft structure absorbs sound energy more effectively. For acoustic partitions, Sucraseal is recommended.
Are both BBA certified?
No. Enverge Sucraseal and Nexseal LE are not BBA certified — their performance is declared to BS EN 14315-1, with BS EN 12086 and BS EN 1602 testing, and BS 476 Part 7 Class 1 fire performance when coated with DC315. Our group company ThermoHoldings Ltd holds BBA certificates 23/6963 and 23/6845 for its ThermoFoam-branded domestic systems (pitched roofs, external walls and suspended timber floors); those certificates are domestic in scope and do not cover commercial work. If your project specifically requires BBA-certified insulation, tell us at enquiry and we will say plainly whether we can meet it.
Get Expert Advice
Not sure which spray foam is right? Duratite provides free specification consultations for commercial projects across the UK. Call 01208 832602 or visit duratite.co.uk/spray-foam-insulation.
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