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Open-Cell vs Closed-Cell Spray Foam: What's the Difference and Which Is Harder to Remove?
- samoconnell48
- 11 hours ago
- 7 min read
If you've been told your spray foam insulation needs to come out, one of the first questions you'll hear from removal companies is: "Do you know if it's open-cell or closed-cell?"
And if you're like most homeowners, your response is probably: "I have absolutely no idea."
Don't worry, you're not alone. Most people who have spray foam in their loft didn't install it themselves, and the previous owner (or cowboy installer) didn't leave a manual. But understanding the difference between open-cell and closed-cell spray foam is crucial, because it affects:
How difficult it is to remove
How much removal will cost
What removal method will be used
The likelihood of underlying damage
This guide will walk you through everything you need to know about both types of spray foam, how to identify which one you have, and what it means for your removal project.
What Is Open-Cell Spray Foam?
Open-cell spray foam (also called low-density or soft foam) is the lighter, spongier type of spray foam insulation.
Key Characteristics:
Density: 0.4–0.6 lb/ft³ (very light)
Texture: Soft, spongy, compressible (like a kitchen sponge)
Appearance: Often yellowish or cream-coloured
R-Value: R3.6–R3.8 per inch (lower insulation value)
Permeability: Semi-permeable (allows some moisture vapour to pass through)
Expansion: Expands up to 100x its liquid volume during application
Common Uses:
Interior walls (soundproofing)
Underfloor insulation
Loft spaces (though less common in the UK)
Why Open-Cell Foam Is Problematic:
While open-cell foam isn't as aggressively problematic as closed-cell, it still causes issues:
1. Moisture Absorption: Because it's semi-permeable, open-cell foam can absorb moisture. If your loft has poor ventilation or a roof leak, the foam acts like a sponge, holding water against timber and causing rot.
2. Compression Damage: Over time, open-cell foam can compress and lose its insulating properties, especially in loft spaces where people walk or store items.
3. Pest Attraction: Rodents and insects can nest in open-cell foam more easily than in closed-cell foam.
4. Still Blocks Ventilation: Even though it's "breathable," it still seals soffits and blocks airflow, which is why surveyors and mortgage lenders flag it.
What Is Closed-Cell Spray Foam?
Closed-cell spray foam (also called high-density or rigid foam) is the harder, denser type of spray foam insulation.
Key Characteristics:
Density: 1.7–2.0 lb/ft³ (much denser and heavier)
Texture: Rock-hard, rigid, not compressible (like hard plastic)
Appearance: Often white, cream, or pale yellow
R-Value: R6.0–R7.0 per inch (higher insulation value)
Permeability: Vapour barrier (completely blocks moisture vapour)
Expansion: Expands 30–40x its liquid volume during application
Common Uses:
Loft insulation (most common in UK lofts)
Cavity wall insulation
Commercial buildings
Flat roofs
Why Closed-Cell Foam Is MORE Problematic:
Closed-cell foam is the type that causes the most serious issues:
1. Complete Vapour Barrier: Because it's completely impermeable, closed-cell foam traps moisture behind it. If there's a roof leak or condensation issue, the moisture can't escape, leading to hidden rot, mould, and structural damage.
2. Aggressive Adhesion: Closed-cell foam bonds so strongly to timber that removing it without damaging the wood underneath is extremely difficult. It can rip splinters out of roof trusses and rafters.
3. Hides Structural Problems: Because it's opaque and rock-hard, closed-cell foam makes it impossible to inspect timber for rot, beetle infestation, or structural issues during surveys.
4. Mortgage Rejection: Lenders are far more cautious about closed-cell foam because of the hidden damage risk. If a surveyor can't inspect the timber, they'll often recommend rejection or demand removal before approving the mortgage.
How to Tell Which Type You Have
If you're not sure which type of spray foam is in your loft, here's
how to identify it:
1. The Touch Test
Open-Cell: Soft and spongy. You can compress it with your hand
(like pressing a sponge).
Closed-Cell: Rock-hard and rigid. You can't dent it with your
hand, it feels like solid plastic.
2. The Visual Test
Open-Cell: Often yellowish or cream-coloured with a more
"fluffy" or irregular surface texture.
Closed-Cell: Usually white or pale cream with a smooth, uniform
surface (though this isn't always reliable).
3. The Density Test
Open-Cell: Lightweight. If you were to remove a small piece, it
would feel like holding a piece of packing foam.
Closed-Cell: Heavy and dense. A small piece would feel solid and weighty.
4. Ask a Professional
If you're still not sure, any spray foam removal company can identify it during a free survey. They'll know instantly by touch and appearance.
Pro tip: Take a photo and send it to removal companies when requesting quotes, they can usually tell from the image.
Which Type Is Harder (and More Expensive) to Remove?
Short answer: Closed-cell foam is significantly harder and more expensive to remove.
Here's why:
Open-Cell Foam Removal:
Method: Manual scraping with hand tools
Difficulty: Moderate (foam is soft, so it scrapes away more easily)
Timber Damage Risk: Lower (foam doesn't bond as aggressively)
Time Required: 2–4 days for an average loft (50–80m²)
Cost: £40–£60 per square metre
Closed-Cell Foam Removal:
Method: Dry ice blasting + manual scraping
Difficulty: High (foam is rock-hard and bonds aggressively to timber)
Timber Damage Risk: Higher (foam can splinter wood when removed)
Time Required: 4–7 days for an average loft (50–80m²)
Cost: £60–£85 per square metre
Why dry ice blasting is used for closed-cell foam:
Dry ice blasting uses compressed air and dry ice pellets (-78°C) to freeze and shatter the foam away from timber. This method is less likely to damage the wood grain compared to aggressive scraping, but it requires specialist equipment and trained operators, hence the higher cost.
Does the Type of Foam Affect Timber Damage?
Yes, absolutely.
Open-cell foam is less likely to have caused timber damage because:
- It's semi-permeable, so some moisture vapour can escape
- It doesn't bond as aggressively, so timber is easier to inspect after removal
- It's more obvious when there's a moisture problem (foam gets visibly wet and heavy)
Closed-cell foam is far more likely to have caused hidden damage because:
- It traps moisture completely, creating ideal rot conditions
- Timber damage can go unnoticed for years because the foam hides it
- By the time the foam is removed, rot may have spread extensively
Statistics:
According to industry data from UK spray foam removal specialists, approximately:
5–20% of open-cell foam removals reveal timber damage requiring repairs
40–50% of closed-cell foam removals reveal timber damage requiring repairs
This is one reason why closed-cell foam is more problematic for mortgage lenders, the risk of expensive structural repairs is much higher.
What Happens If You Have Closed-Cell Foam?
If you've confirmed you have closed-cell foam, here's what to expect:
1. Higher Removal Costs
Budget for the upper end of removal costs (£60–£85/m²) due to the specialist equipment and labour required.
2. Structural Survey Recommended
Before committing to removal, get a structural survey to assess timber condition. If there's extensive rot, you may need to factor in £5,000–£15,000+ in structural repairs.
3. Longer Timeline
Closed-cell foam removal takes longer, expect 4–7 days for an average loft, compared to 2–4 days for open-cell.
4. More Waste
Closed-cell foam is denser, so there's more material to dispose of (and disposal costs are calculated by weight).
5. Potential for Timber Splintering
Even with dry ice blasting, there's a risk of timber damage during removal. Make sure your contractor is experienced and insured.
What Happens If You Have Open-Cell Foam?
If you have open-cell foam, you're in a slightly better position:
1. Lower Removal Costs
Expect £40–£60/m² for removal (still expensive, but cheaper than closed-cell).
2. Faster Removal
Open-cell foam scrapes away more easily, so the job is quicker (2–4 days).
3. Lower Timber Damage Risk
You're less likely to find extensive rot, though it's still possible if there's been a roof leak.
4. Easier DIY? (Still Not Recommended)
Some homeowners attempt DIY removal of open-cell foam because it's softer. We still strongly advise against this due to health risks (foam dust is a respiratory irritant) and the need for professional waste disposal.
Can You Mix Open-Cell and Closed-Cell Foam?
In rare cases, yes, some installers have used both types in different areas of the same loft. For example:
Closed-cell on the roof slope (for insulation)
Open-cell on gable walls (for soundproofing)
If you suspect you have both types, point this out to removal companies during the survey so they can quote accurately.
Does It Matter for Mortgage Lenders?
Yes and no.
Most mortgage lenders don't distinguish between open-cell and closed-cell foam in their lending criteria, they flag any spray foam in the loft as a potential issue. However:
Closed-cell foam is more likely to result in an outright mortgage rejection because of the higher hidden damage risk.
Open-cell foam may be accepted by some lenders if a structural survey confirms no timber damage, but this is rare and depends on the lender's policy.
In practice, if you're selling a property with spray foam (of any type), expect buyers' mortgage lenders to demand removal or significantly reduce the property valuation.
Which Type Should You Remove First?
If you're planning to sell, remove whichever type you have as soon as possible. Don't wait until a buyer's survey flags it, by then, you've already lost the sale and your negotiating position.
If you're staying in the property long-term and have both types in different areas, prioritise closed-cell foam removal because of the higher structural damage risk.
Open Cell vs Closed Cell Spray Foam: Final Thoughts
Understanding the difference between open-cell and closed-cell spray foam won't make removal any less frustrating or expensive, but it will help you:
Get accurate quotes from removal companies
Understand why costs vary
Anticipate potential timber damage
Plan your timeline and budget
The bottom line: Whether you have open-cell or closed-cell foam, if it's causing mortgage issues or you're planning to sell, removal is your best option.
Need spray foam removed? Contact Remove Spray Foam for a free, no-obligation survey. We'll identify which type of foam you have, assess your loft's condition, and provide a detailed fixed-price quote for removal.
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