Open Cell vs Closed Cell Spray Foam Insulation: What's the Difference?
Understanding the two types—and why it matters for removal and lender approval
Why This Matters
If you have spray foam insulation in your roof, knowing whether it's open cell or closed cell affects:
- • Removal difficulty and cost (closed cell is harder to remove)
- • Risk of hidden timber damage (closed cell creates higher moisture risk)
- • Lender attitudes (both types cause issues, but closed cell faces more scrutiny)
- • Removal methods required (different techniques for each type)
The Two Types: Side-by-Side Comparison
| Characteristic | Open Cell | Closed Cell |
|---|---|---|
| Structure | Cells are broken/open (like a sponge) | Cells are sealed/closed (solid barrier) |
| Density | 0.4-0.6 lb/ft³ (soft, compressible) | 1.7-2.0 lb/ft³ (rigid, hard) |
| Appearance | Light yellow/cream, fluffy texture | Pale yellow/white, dense and hard |
| R-Value (insulation) | R-3.5 to R-3.7 per inch | R-6 to R-7 per inch (better) |
| Vapour Permeability | Breathable (allows moisture movement) | Vapour barrier (blocks moisture) |
| Water Absorption | High (absorbs water like a sponge) | Very low (water-resistant) |
| Typical Cost (installation) | £15-25 per m² | £25-40 per m² (more expensive) |
| Removal Difficulty | Moderate (softer, easier to cut) | High (extremely hard, adheres strongly) |
| Removal Cost | £4,000-8,000 (typical house) | £6,000-12,000+ (20-40% higher) |
| Lender Acceptance | Rejected (blocks inspection) | Rejected (worse due to moisture risk) |
Open Cell Spray Foam: The "Softer" Option
How It Works
Open cell foam expands significantly when applied (up to 100x its liquid volume), creating a lightweight, spongy material with broken cell walls. Air and moisture can move through the cells.
Advantages (During Installation)
- ✓ Less expensive than closed cell
- ✓ Better sound dampening (softer material absorbs noise)
- ✓ More flexible (moves with building settlement)
- ✓ Uses less material to fill the same space
Problems for Homeowners
- ✗ Absorbs water—if leaks occur, foam holds moisture against timber (rot risk)
- ✗ Still blocks roof ventilation (lender concern)
- ✗ Prevents visual timber inspection (mortgage issue)
- ✗ Can sag or deteriorate over time in loft conditions
Removal Considerations (Open Cell)
Easier to remove: Open cell foam can be cut and pulled away more readily than closed cell. It's still labour-intensive, but requires less aggressive manual work.
- • Method: Hand tools (scrapers, chisels, knives)
- • Time: 3-7 days for average house
- • Timber damage risk: Lower (foam doesn't adhere as aggressively)
- • Cost: £4,000-8,000 typically
Closed Cell Spray Foam: The "Industrial Strength" Option
How It Works
Closed cell foam has tightly packed cells that don't allow air or moisture to pass through. It's dense, rigid, and acts as both insulation and a structural reinforcement.
Advantages (During Installation)
- ✓ Superior insulation value (R-6 to R-7 per inch)
- ✓ Acts as vapour barrier (no additional membrane needed)
- ✓ Adds structural strength to roof
- ✓ Water-resistant (doesn't absorb moisture like open cell)
- ✓ Longer lifespan (doesn't degrade as quickly)
Problems for Homeowners
- ✗ Complete vapour barrier = any moisture behind it is trapped (serious rot risk)
- ✗ Blocks ALL roof ventilation (worse than open cell)
- ✗ Impossible to inspect timber without removal
- ✗ Lenders view it as higher risk due to moisture trapping
- ✗ Extremely difficult and expensive to remove
- ✗ Can hide catastrophic timber damage for years
Removal Considerations (Closed Cell)
Much harder to remove: Closed cell adheres extremely strongly to timber. Manual removal requires significant physical labour and specialist tools.
- • Method: Heavy-duty hand chisels, scrapers (mechanical tools damage timber)
- • Time: 5-10 days for average house (20-40% longer than open cell)
- • Timber damage risk: Higher—foam bonds so tightly it can pull wood fibres when removed
- • Cost: £6,000-12,000+ (significantly more than open cell)
- • Worker fatigue: Extremely physically demanding—affects quality if rushed
How to Tell Which Type You Have
Visual Inspection
Open Cell
- • Light yellow or cream colour
- • Spongy, soft texture
- • Compressible when pressed
- • Often fluffy or irregular surface
Closed Cell
- • Pale yellow, white, or beige
- • Hard, rigid texture
- • Cannot compress (like solid plastic)
- • Smooth, dense surface
Physical Test (If Accessible)
Gently press the foam with your finger:
- • Open cell: Compresses easily, springs back slowly (like memory foam)
- • Closed cell: Does not compress—feels like hard plastic or dense rubber
Check Installation Records
If you have documentation from the original installation:
- • Installer invoice or specification sheet
- • Product name (e.g., "Icynene" is often open cell, "Kingspan" often closed cell)
- • Property survey from when you bought the house
Not Sure?
If you can't determine the type, assume closed cell when getting removal quotes. It's better to budget for the more expensive option and be pleasantly surprised than the reverse.
Impact on Lender Approval
Both Types Face Lender Rejection
Important: UK mortgage lenders generally reject properties with EITHER type of spray foam insulation applied to roof timber.
However, closed cell often faces stricter scrutiny because:
- • Complete vapour barrier = higher condensation and rot risk
- • Harder to inspect even with sampling (adheres too strongly)
- • More likely to hide serious timber deterioration
- • Property Care Association guidance specifically warns against closed cell under tiles/slates
What This Means for You
Regardless of foam type, if you're selling or remortgaging, you'll likely need:
- 1. Complete removal using manual hand tools
- 2. Independent surveyor inspection of all timber
- 3. Any necessary timber repairs
- 4. Restoration of proper roof ventilation
- 5. RICS or PCA certification that the work is compliant
The type of foam only affects the cost and duration of step 1 (removal).
Cost Comparison: Removal Estimates
Typical removal costs by property size:
Costs include removal, waste disposal, and basic certification. Timber repairs are additional if needed.
Key Takeaways
- ✓ Open cell is softer, cheaper to install and remove, but absorbs moisture
- ✓ Closed cell is harder, more effective insulation, but much more difficult to remove
- ✓ Both types cause lender rejection due to inspection and ventilation concerns
- ✓ Closed cell typically costs 20-40% more to remove due to labour intensity
- ✓ Either type requires the same certification process after removal
- ✓ Knowing which you have helps you get accurate quotes and realistic timelines
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