Insulation Types: Which One Should You Choose?

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

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.

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.

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:

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?

Fire Safety Ratings Explained

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.