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Insulation materials · PUR / PIR
PUR / PIR: the highest insulating power per centimetre
When every centimetre counts, polyurethane (PUR) and polyisocyanurate (PIR) take the lead. With a lambda among the lowest on the market (~0.022 W/mK), these rigid boards reach a high thermal resistance in a slim thickness — the solution for floors under screed, balconies and roofs in sarking.
- λ 0.022–0.028
- W/mK conductivity
- Rigid board
- with kraft/alu facing
- Floor & sarking
- favoured uses
Lambda ~0.022the lowest on the market
Slim thicknesswhere space is tight
Technical specs
What a PUR / PIR board is really worth
The hard facts about a high-performance rigid insulant installed by our teams. Useful figures for comparison, not marketing.
- Conductivity (lambda) 0.022–0.028 W/mK
This is the lowest lambda of the common insulants. The lower the value, the more the material slows heat: at equal thermal resistance (R), PUR/PIR needs far less thickness than wool or cellulose.
- Thickness for R = 4.5 ~10 cm
Where mineral wool needs 16 to 18 cm, a PIR board reaches the same resistance with about 10 cm. Decisive under a screed, on a balcony or in sarking, when every centimetre of height counts.
- Form & facing Rigid board
Rigid sheets covered with a kraft, glass-fleece or aluminium facing that acts as a vapour barrier and reflector. Straight or tongue-and-groove edges to limit thermal bridges between boards.
- Mechanical strength Resistant
Its rigidity supports a screed or a floor: you insulate a floor with no settling over time. The board keeps its thickness and performance under load, unlike soft insulants.
- Moisture behaviour Closed cell
The closed-cell structure absorbs very little water and keeps its performance in a damp environment. An asset in floors, cellars or under roofs, provided the joint airtightness is well handled.
- Fire behaviour PIR > PUR
PIR resists fire better and gives off less smoke than PUR: it’s the variant to prefer. Both remain petroleum-based materials to be classified correctly according to the wall and the regulations.
* Indicative values for common-range boards. The exact lambda depends on the facing and the density; the thickness is calculated from the target thermal resistance (R) — confirmed during the survey.
Full transparency
PUR / PIR: strengths & limits
No insulant is perfect for every wall. Here, honestly, is where PUR/PIR excels and where a wool or wood fibre will fit better.
Where it shines
- The best insulating powerThe lowest lambda of the common range: maximum R per centimetre.
- Slim thicknessIdeal when height is tight: floors under screed, sarking, balconies, thresholds.
- Rigid and load-bearingSupports a screed or a floor without settling or losing its performance.
- Insensitive to moistureClosed cells: very low water uptake, stable performance over time.
What you should know
- Petroleum-based materialHigh embodied energy and petrochemical origin: less eco-friendly than fibres.
- Limited summer comfortLow thermal lag: heat crosses quickly, unlike cellulose or wood fibre.
- Fire behaviourCombustible with smoke to watch; PIR does better than PUR, to classify according to the wall.
- Airtightness to handleThe joints between boards must be treated, or air and heat will leak.
Which project
Is PUR / PIR right for you?
It comes into its own whenever space is tight and you need maximum performance in little thickness. A few cases where it shines:
-
Floor insulation under screed
Under a screed or underfloor heating, the rigidity and low lambda of PUR/PIR insulate without eating into the ceiling height. The reference in floor renovation.
-
Roof in sarking
Laid above the rafters, the rigid boards eliminate the roof frame’s thermal bridges and preserve the attic volume. PIR excels here thanks to its slim thickness.
-
Balconies, thresholds, low height
Anywhere every centimetre counts — balconies, door thresholds, drops — PUR/PIR delivers the expected thermal resistance without any awkward over-thickness.
Summer comfort or an eco choice?
If thermal lag and summer comfort come first, look instead at cellulose. For a versatile price-to-performance ratio, mineral wool remains a safe bet.
Glissez la poignée pour comparer
Real case · floor renovation, Namur
A ground floor insulated without losing height thanks to 8 cm of PIR
The ground-floor slab sat over an unheated cellar, a source of cold feet and heat loss. Raising the floor much was out of the question. We laid 8 cm of aluminium-faced PIR boards under a flowing screed: a high thermal resistance in a minimal thickness, and comfort restored from the very next winter.
- 8 cmof thickness only
- R ~3.6m²K/W in the floor
- −25%of loss through the floor
Customer reviews
They chose wendows
4.5/5 · 2verified reviews
« Insufflation des murs creux, rapide et sans dégât. La prime régionale a couvert une bonne part. Maison nettement moins froide. »
David K.Huy
Compare the materials
PUR / PIR, or another insulant?
PUR/PIR wins on lambda and thickness; fibres win on summer comfort and ecology. Compare point by point, then open the material that matches your wall.
| Critère | PUR / PIRVous êtes ici | Mineral woolVoir la gamme → | CelluloseVoir la gamme → |
|---|---|---|---|
| Lambda (conductivity) | 0.022–0.028 — the lowest | 0.032–0.040 | 0.038–0.042 |
| Thickness at equal R | The slimmest | Medium | Thicker |
| Fire behaviour | Combustible (PIR > PUR) | Non-combustible | Well treated (salts) |
| Summer comfort / thermal lag | Low | Medium | Excellent |
| Ecology / embodied energy | Petroleum-based, high | Average | Recycled, low |
| Moisture resistance | Excellent (closed cell) | Sensitive if wet | Regulates vapour |
| Ideal for | Floors, sarking, slim thickness | Walls, attics, versatile | Attics, summer comfort |
Indicative benchmarks for common ranges. The right insulant depends on the wall, the available space and the budget — we fine-tune it together during the survey.
- overview
All the materials
Wool, cellulose, PUR/PIR, wood fibre: compare the insulants to pick the right one for each wall of your home.
Compare the materials → - vs PUR/PIR
Mineral wool
Non-combustible and versatile, the best price-to-performance ratio for walls and attics. Thicker at equal R.
Compare with wool → - vs PUR/PIR
Cellulose
A recycled insulant with unbeatable thermal lag: the best summer comfort. The eco-friendly alternative to PUR/PIR.
Discover cellulose → - application
Floor insulation
PUR/PIR’s favourite use: under a screed or over a cellar, insulating the floor without losing height.
See floor insulation → - application
Roof sarking
Rigid boards above the rafters: zero roof-frame thermal bridge and attics preserved.
Discover sarking → - ↑ category
All about insulation
An overview of our insulation solutions in Belgium: walls, roof, floor, materials, installation and grants on one page.
Back to the insulation guide →
Indicative 2026 pricing
How much does PUR / PIR insulation cost?
The price depends on the thickness, the facing and the application. PUR/PIR costs more per square metre than fibres, but saves on thickness. Here are some benchmarks for installed insulant.
See the detailed insulation price list →* Indicative ranges per m² supplied and installed, excluding substrate preparation. A costed estimate is provided with your free quote.
- PUR/PIR board €20–35/m²supplied, by thickness
- Installed floor insulation from €35/m²boards + installation
- Renovation grant up to 35%of the amount, depending on your income
- Reduced VAT 6%for renovation (home > 10 years old)
PUR / PIR FAQ
Your questions about PUR / PIR
What’s the difference between PUR and PIR? +
Both are rigid closed-cell foams, highly insulating. PIR (polyisocyanurate) is an evolution of PUR (polyurethane): it resists fire better and gives off less smoke, with similar thermal performance. Given the choice, we favour PIR, especially in roofs and exposed walls.
Why does PUR/PIR insulate with so little thickness? +
Because its lambda (thermal conductivity) is the lowest of the common insulants, around 0.022 W/mK. At equal thermal resistance, it needs almost half the thickness of mineral wool. That’s the decisive asset when height is tight, such as under a screed or on a balcony.
Is PUR/PIR suitable for insulating a floor? +
Yes, it’s its favourite use. Its rigidity supports a screed or a floor without settling, and its low lambda insulates a floor over a cellar or on the ground without eating into the ceiling height. It is also laid under underfloor heating.
Is PUR/PIR good for summer comfort? +
This is its main limit: its thermal lag is low, heat crosses quickly. For summer comfort in attics, cellulose or wood fibre is far more effective. PUR/PIR is justified above all by its winter performance in little thickness.
Does PUR/PIR dislike moisture? +
Very little: its closed-cell structure absorbs almost no water and keeps its performance in a damp environment, which makes it a good choice in floors, cellars or under roofs. It remains essential to handle airtightness by treating the joints between boards.
What grants are available for PUR/PIR insulation? +
Grants depend on the thermal resistance (R) achieved and the wall insulated, not on the material. High-performance floor or roof insulation qualifies, depending on your region and income, for a renovation grant and the 6% VAT rate for homes over ten years old. We handle the paperwork for you.
Get your free PUR / PIR insulation quote within 48h
Free on-site survey, grants calculated, a single point of contact. Describe your project in under a minute.
- Free and no obligation
- Grants & 6% VAT handled for you
- Installed by our certified installers