PIR vs EPS vs XPS Floor Insulation: Which Should You Use?
PIR, EPS (expanded polystyrene) and XPS (extruded polystyrene) are the three rigid boards most often used to insulate floors. They differ in how well they insulate per millimetre, how much load they take, how they handle moisture and what they cost. This guide compares them using manufacturers' published figures and live prices, so you can pick the right board for your floor.
Quick answer
- PIR insulates best per millimetre (λ 0.022 W/mK), so choose it when floor height is tight. It's the usual choice between joists in suspended timber floors and above or below slabs under screed.
- EPS costs the least per square metre, but you need more thickness for the same U-value. Choose the grade (EPS 70, 100 or 150) to suit the loads.
- XPS combines high compressive strength (300 kPa for Kingspan GreenGuard GG300) with low water absorption, so it's the one to choose where boards may get wet or take heavy loads, such as below a slab.
Side-by-side comparison
| PIR (Recticel Eurothane GP) | EPS (EPS 70 / 100 / 150) | XPS (Kingspan GreenGuard GG300) | XPS (Jackon JACKODUR KF 300) | |
|---|---|---|---|---|
| Thermal conductivity (λ) | 0.022 W/mK | Not published for the unbranded boards we stock | 0.033 W/mK | 0.034–0.036 W/mK, depending on thickness |
| R-value at 100mm | 4.50 m²K/W | Not published | 3.00 m²K/W | 2.85 m²K/W |
| Compressive strength | ≥120 kPa | Grade number = kPa at 10% deformation | 300 kPa | Up to 300 kPa |
| Reaction to fire | Euroclass F | Not published | Euroclass F | Euroclass E |
| Board size | 2400 × 1200mm | 2400 × 1200mm | 1250 × 600mm | 1250 × 600mm |
| Price per m², 100mm (ex VAT, at the time of writing) | £12.44 | EPS 70 £6.51, EPS 100 £9.26, EPS 150 £11.72 | £21.24 | £18.33 |
The EPS boards we stock are unbranded, so we can't quote a manufacturer's λ or fire classification for them, and we've left those cells blank rather than guess. The grade name tells you the compressive stress: an EPS 100 board is rated at 100 kPa at 10% deformation.
Thickness for the same thermal resistance
Because the λ values differ, you need different thicknesses to get the same R-value. Using the manufacturers' published R-values:
| Board | Thickness for R ≈ 4.5 m²K/W |
|---|---|
| Recticel Eurothane GP / Kingspan TP10 (PIR) | 100mm (R 4.50) |
| Kingspan GreenGuard GG300 (XPS) | 150mm (R 4.50) |
| Jackon JACKODUR KF 300 (XPS) | 160mm (R 4.55); we stock up to 140mm |
So XPS needs about half as much thickness again as PIR for the same performance. If floor height is very tight, the phenolic Kingspan Kooltherm K103 goes further still. See our K103 vs PIR comparison.
PIR: best insulation per millimetre
PIR boards such as Recticel Eurothane GP 100mm (£35.83 per 2.88m² sheet) and Kingspan TP10 100mm (£51.66) are the usual choice when you need to hit a U-value without raising the floor much. They're used between the joists of suspended timber floors and above or below concrete slabs. For timber floors, see what thickness of PIR for a suspended timber floor.
EPS: the budget option, graded by strength
EPS is the cheapest of the three per square metre. The trade-off is thickness: you need more of it for the same U-value, which matters if you're matching existing floor levels. Choose the grade to suit the floor loads:
Where a floor designer or screed supplier specifies a grade, use that. Each grade comes in 25, 50, 75, 100 and 150mm thicknesses.
XPS: strength and moisture resistance
XPS has a closed-cell structure, and both manufacturers highlight its low water absorption. Jackon's datasheet gives long-term water absorption by total immersion of ≤0.7% by volume for JACKODUR KF 300, and lists under-slab insulation, under-screed insulation, basement perimeter walls and inverted roofs among its uses. Kingspan GreenGuard GG300 has a declared compressive strength of 300 kPa. Choose XPS where boards sit below the slab, may be exposed to ground moisture, or carry heavy loads.
Frequently asked questions
Which is best under a screed?
All three are used under screeds. PIR gives the thinnest build-up. EPS is the cheapest, if you have the depth and choose a suitable grade. XPS suits heavier loads or wetter conditions. Follow the screed or floor designer's specification, and fit an edge strip such as our screed edging strip around the perimeter.
Is XPS better than PIR?
Not for insulation per millimetre, where PIR wins: 100mm of PIR has an R-value of 4.50 against 3.00 for 100mm of GG300. XPS is better for compressive strength and moisture resistance.
Do I need a damp-proof membrane?
Most ground floors need one, and where it goes depends on the floor design and the insulation manufacturer's guidance. We stock damp-proof membrane and vapour control layer.
How thick should floor insulation be?
It depends on the U-value you need and the floor's perimeter-to-area ratio. Use our PIR U-value calculator, and see what thickness of PIR insulation you need.
Order floor insulation
Browse all floor insulation boards, including PIR, EPS and Jackon XPS. Prices are shown ex VAT. We are delivery only (no collection) and deliver to mainland England and Wales, with a £400 ex VAT minimum order and free delivery on every order (see delivery information). Call us on 03330 908479 (Mon–Thu 8am–5pm, Fri 8am–12pm), email sales@insulationwarehousedirect.co.uk, or order online.
Sources: Recticel Eurothane GP product page; Kingspan Thermapitch TP10 brochure; Kingspan GreenGuard brochure and GG300 Declaration of Performance; Jackon JACKODUR KF 300 Standard technical data. EPS grade designations follow BS EN 13163. Figures are indicative and correct at the time of writing.