Open Cell vs Closed Cell Spray Foam: Which is Worse for Your Home?
Understanding the differences and risks
The Unfortunate Answer
Both types cause the same mortgage and insurance problems. UK lenders and insurers don't distinguish between open cell and closed cell—both are treated as unacceptable spray foam insulation.
What's the Difference?
Open Cell Foam
- •Structure: Spongy, porous, air-filled cells
- •Density: Low (0.4-0.6 lbs per cubic foot)
- •Expansion: Expands 100x original volume
- •Vapor permeability: Breathable
- •Cost: Lower (£20-35 per m²)
- •Common in UK: More frequently installed
Closed Cell Foam
- •Structure: Dense, rigid, sealed cells
- •Density: High (1.7-2.0 lbs per cubic foot)
- •Expansion: Expands 30x original volume
- •Vapor permeability: Non-breathable vapor barrier
- •Cost: Higher (£40-60 per m²)
- •Common in UK: Less frequently installed
Mortgage & Insurance Impact: No Difference
From a lending and insurance perspective, both types create identical problems:
Key point: Lenders and insurers care that spray foam exists—not which type it is. Both require removal for property transactions.
Technical Differences in Risk
Open Cell: Moisture Absorption Risk
Open cell foam is breathable and can absorb moisture if installed improperly or if roof leaks occur. This trapped moisture can lead to timber rot.
Risk level: Higher risk of moisture-related timber damage, but damage is often detectable earlier through visible sagging or water stains.
Closed Cell: Hidden Moisture Trapping
Closed cell foam creates a complete vapor barrier. If any moisture gets trapped during installation or enters later, it has nowhere to escape and remains against timber indefinitely.
Risk level: Lower frequency of problems, but when issues occur, they're often more severe and go undetected longer.
Removal Difficulty: Which is Harder?
Open Cell Foam Removal
Difficulty: Easier (relatively speaking)
- ✓Softer, spongy texture makes manual removal faster
- ✓Peels away from timber more readily
- ✓Typically costs 20-30% less to remove
Average cost: £3,000 - £8,000
Closed Cell Foam Removal
Difficulty: Significantly harder
- ✗Dense, rigid structure requires more aggressive chiseling
- ✗Bonds more strongly to timber surfaces
- ✗Takes 30-50% longer to remove manually
- ✗Higher risk of timber damage during removal due to strong adhesion
Average cost: £5,000 - £15,000
⚠️ "Sold as Better" Doesn't Mean Safe
Many homeowners were told closed cell foam is "premium" or "better quality." While it does have superior insulation properties, this is irrelevant to the fundamental problems:
- •Lenders still won't accept it
- •Insurance still won't cover it
- •It's more expensive to remove
- •Property value still drops
The Bottom Line
If you're deciding which to install: Don't install either. The mortgage/insurance problems are identical.
If you already have it: The type doesn't matter for property transactions—both require removal.
If you're budgeting removal: Open cell is cheaper and faster to remove; closed cell costs more and takes longer.
Either way, removal is the only solution to restore full property value and mortgageability.
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