# Insulation Types: Which One Should You Choose?

> Compare insulation types: mineral wool, PIR board, spray foam, sheep wool, cellulose. Thermal performance, fire ratings, costs, and best use cases.

Canonical: https://renoquant.com/insulation-types-guide
Prices updated: 2026-03

## Comparing Insulation Types

Choosing the right insulation type affects thermal performance, installation cost, fire safety, and long-term durability. This guide compares every major insulation material available in Europe, with data on thermal conductivity, fire ratings, moisture handling, and ideal use cases.

### Complete Insulation Comparison Table

| Property | Glass Mineral Wool | Rock Mineral Wool | PIR Board | EPS | XPS | Open-Cell Spray Foam | Closed-Cell Spray Foam | Sheep Wool | Cellulose |
|----------|-------------------|-------------------|-----------|-----|-----|---------------------|----------------------|------------|-----------|
| Thermal conductivity (W/mK) | 0.044 | 0.038 | 0.022 | 0.034 | 0.029 | 0.038 | 0.025 | 0.038 | 0.040 |
| R-value per 100mm | 2.27 | 2.63 | 4.55 | 2.94 | 3.45 | 2.63 | 4.00 | 2.63 | 2.50 |
| Fire rating (Euroclass) | A1 | A1 | B-C | E | E | B-C | B-C | B-D | B-C |
| Moisture handling | Hydrophobic | Hydrophobic | Closed cell | Absorbs | Closed cell | Open cell | Vapour barrier | Absorbs/releases | Absorbs/releases |
| Cost per m2 (100mm) | EUR 3-5 | EUR 5-8 | EUR 12-22 | EUR 5-10 | EUR 8-15 | EUR 20-35 | EUR 35-55 | EUR 12-22 | EUR 8-15 |
| DIY friendly | Yes | Yes | Yes | Yes | Yes | No | No | Yes | No (blown) |
| Lifespan | 40-50 years | 40-50 years | 50+ years | 30-50 years | 50+ years | 25-50 years | 50+ years | 40-50 years | 30-40 years |

### Mineral Wool (Glass Wool and Rock Wool)

Mineral wool is the most widely used insulation in Europe. Glass wool is made from recycled glass, rock wool from volcanic basite rock. Both are non-combustible (A1 fire rating), affordable, and easy to cut and install.

**Glass wool** is lighter and cheaper, making it the standard choice for loft rolls. **Rock wool** is denser, offers slightly better thermal performance (0.038 vs 0.044 W/mK), and provides superior acoustic insulation and fire resistance. Rock wool is preferred for wall insulation and fire-rated applications.

| Feature | Glass Wool | Rock Wool |
|---------|-----------|-----------|
| Thermal conductivity | 0.044 W/mK | 0.038 W/mK |
| Density | 10-20 kg/m3 | 30-200 kg/m3 |
| Fire resistance | A1 (melts at 600C) | A1 (melts at 1000C+) |
| Acoustic performance | Good | Excellent |
| Cost (100mm) | EUR 3-5/m2 | EUR 5-8/m2 |
| Best for | Loft rolls, budget projects | Walls, acoustic, fire barriers |

Both types cause skin irritation during handling. Wear long sleeves, gloves, a dust mask, and eye protection when installing mineral wool.

### PIR Board (Celotex, Kingspan, Recticel)

PIR (polyisocyanurate) rigid foam boards are the go-to choice when you need maximum insulation in minimum thickness. At 0.022 W/mK, PIR is twice as thermally efficient as mineral wool — 50mm of PIR equals 100mm of mineral wool.

PIR boards come in standard 1200x2400mm sheets and cut cleanly with a fine-tooth saw. They are commonly used for:

- Internal wall insulation (bonded to plasterboard as a laminate)
- Floor insulation between joists
- Flat roof insulation above the deck
- Pitched roof insulation between rafters (where depth is limited)

**Limitation:** PIR is not A1 fire-rated. It must always be covered with plasterboard or another fire barrier. It is also more expensive per m2 than mineral wool, though this is partly offset by needing only half the thickness.

### Spray Foam Insulation

Spray foam is applied as a liquid that expands and cures into a rigid or semi-rigid foam. It fills every gap and crack, creating an airtight insulation layer.

| Feature | Open-Cell Spray Foam | Closed-Cell Spray Foam |
|---------|---------------------|----------------------|
| Thermal conductivity | 0.038 W/mK | 0.025 W/mK |
| Density | 8-15 kg/m3 | 30-60 kg/m3 |
| Vapour barrier | No | Yes |
| Structural strength | Low | High (adds rigidity) |
| Moisture resistance | Low (absorbs water) | High (closed cells) |
| Cost per m2 (100mm) | EUR 20-35 | EUR 35-55 |
| Best for | Lofts, stud walls | Roofs, basements, cold stores |

**Important warnings about spray foam:**

- Some mortgage lenders will not lend on properties with spray foam on the roof — it can mask structural problems and prevent roof inspection
- Poorly applied spray foam can trap moisture and cause timber rot
- Removal is extremely difficult and expensive (EUR 3,000-8,000 for a typical loft)
- Always use a certified installer who offers a 25-year guarantee

### Natural and Eco-Friendly Insulation

For environmentally conscious projects, several natural alternatives perform well:

| Material | Source | Thermal Conductivity | Key Advantage | Key Limitation |
|----------|--------|---------------------|---------------|----------------|
| Sheep wool | Waste sheep fleece | 0.038 W/mK | Absorbs/releases moisture naturally | 3-4x cost of mineral wool |
| Cellulose | Recycled newspaper | 0.040 W/mK | Low embodied carbon, blown into cavities | Professional installation only |
| Wood fibre | Softwood waste | 0.038 W/mK | Excellent summer heat protection | Heavyweight, needs strong fixings |
| Hemp | Hemp plant fibres | 0.040 W/mK | Carbon-negative crop, breathable | Limited availability, higher cost |
| Cork | Cork oak bark | 0.040 W/mK | Waterproof, renewable, very durable | Expensive, limited supply |

Sheep wool is the most practical natural option for DIY installation. It comes in rolls and batts like mineral wool, handles easily without protective equipment (no skin irritation), and naturally regulates humidity by absorbing up to 35% of its weight in moisture without losing thermal performance.

### Which Insulation for Which Location?

| Location | Best Choice | Why | Alternative |
|----------|------------|-----|-------------|
| Loft (between joists) | Glass mineral wool rolls | Cheapest, easiest to lay, A1 fire rated | Sheep wool rolls |
| Loft (over joists) | Glass mineral wool rolls | Same as above | Cellulose (blown) |
| Cavity wall | Blown mineral wool or EPS beads | Professional cavity fill, proven track record | — |
| Solid wall (internal) | PIR board + plasterboard laminate | Thinnest option, preserves room space | Rock wool in stud frame |
| Solid wall (external) | EPS or mineral wool with render | Full coverage, no loss of internal space | Wood fibre boards |
| Timber floor (from below) | Mineral wool batts with netting | Affordable, easy to fit between joists | PIR board cut to fit |
| Concrete floor | PIR board | Moisture resistant, high R-value per mm | XPS (under slab) |
| Flat roof | PIR board | Moisture resistant, lightweight | — |
| Pitched roof (rafters) | PIR board between rafters | Maximises headroom in loft conversion | Mineral wool batts |
| Stud wall (partition) | Rock mineral wool batts | Best acoustic performance for the price | Sheep wool batts |

### Fire Safety Ratings Explained

| Euroclass | Description | Insulation Types | Use Restrictions |
|-----------|-------------|-----------------|-----------------|
| A1 | Non-combustible | Mineral wool, rock wool | None — safe everywhere |
| A2 | Very limited combustibility | Some rock wool products | None for most applications |
| B | Limited combustibility | PIR board, some spray foams | Must be covered by fire barrier (plasterboard) |
| C | Combustible, limited contribution | Some PIR, some spray foams | Must be covered, not for high-rise above 18m |
| D | Combustible, medium contribution | Wood fibre, some hemp | Restricted use in multi-storey buildings |
| E | Highly combustible | EPS, XPS (untreated) | Not permitted in walls of buildings over 18m |

Since the Grenfell Tower fire in 2017, regulations on combustible insulation materials in buildings over 18 metres (approximately 6 storeys) have been significantly tightened across Europe. For high-rise projects, only A1 or A2 rated materials are permitted in external walls.

### Making Your Decision

Choose your insulation based on these priorities:

1. **Tightest budget** — Glass mineral wool. Cheapest per R-value, widely available, A1 fire rated.
2. **Limited space** — PIR board. Half the thickness of mineral wool for the same R-value.
3. **Best acoustic performance** — Rock mineral wool. Dense, excellent at absorbing sound.
4. **Eco-friendly** — Sheep wool or cellulose. Low embodied carbon, natural moisture management.
5. **Awkward shapes and gaps** — Spray foam. Fills every void, creates airtight seal.
6. **Maximum fire safety** — Rock mineral wool. A1 rated, withstands temperatures above 1000 degrees C.

## Frequently Asked Questions

### What is the difference between mineral wool and PIR insulation?

Mineral wool (glass wool or rock wool) is a soft, flexible material that comes in rolls and batts, best for lofts and stud walls. PIR (polyisocyanurate) is a rigid foam board brand-named as Celotex or Kingspan. PIR has double the thermal performance per millimetre (0.022 W/mK vs 0.044 W/mK), making it ideal where space is limited, such as wall and floor insulation. Mineral wool is much cheaper per m2 at the same R-value.

### Is spray foam insulation worth it?

Spray foam provides excellent coverage in awkward spaces and creates an airtight seal. However, it costs 3-5 times more than mineral wool, can cause problems with mortgage valuations and roof tile integrity, and is very difficult to remove if issues arise. It is worth considering for hard-to-reach areas or where airtightness is critical, but for standard lofts, mineral wool is usually the better choice.

### Which type of insulation is best for each location in the home?

Lofts: mineral wool rolls (cheapest, easiest DIY). Cavity walls: blown mineral wool or EPS beads (professional only). Internal solid walls: PIR board with plasterboard laminate (thinnest option). Floors: PIR board between joists or mineral wool batts supported by netting. Flat roofs: PIR board (moisture resistant). Pitched roof rafters: mineral wool batts or spray foam.

### What fire rating does insulation need?

Insulation should be at least Euroclass A1 or A2 (non-combustible) for use in walls, floors, and ceilings. Mineral wool and rock wool are A1 rated (they do not burn at all). PIR board is typically B or C rated (limited combustibility) and must be covered with plasterboard as a fire barrier. Spray foam varies from B to E rating depending on the product. After the Grenfell fire, regulations on combustible insulation in high-rise buildings have been significantly tightened.

### Is natural insulation (sheep wool, cellulose) as effective as synthetic?

Yes, natural insulation products achieve similar thermal performance to synthetic alternatives. Sheep wool has a thermal conductivity of 0.038 W/mK (slightly better than glass wool at 0.044 W/mK). Cellulose is 0.040 W/mK. Natural products also handle moisture better — sheep wool can absorb and release moisture without losing performance. The trade-off is higher cost: sheep wool costs 3-4 times more than mineral wool per m2.

### Can I mix different types of insulation?

Yes, mixing insulation types is common and sometimes recommended. For example, you might use mineral wool between loft joists and PIR board above them for a thinner overall build-up. In walls, PIR board is often used as the main insulation with mineral wool filling gaps around pipes and in awkward corners. The key rule is to never trap a vapour barrier between two insulation layers, as this can cause condensation.

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Interactive version with calculator: https://renoquant.com/insulation-types-guide. Figures are estimates; final quotes vary by site conditions, materials, and region.