Sandwich panel stack - EPS, rock wool and PU insulated composite wall and roof panels

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Sandwich Panel Core Comparison:
EPS vs Rock Wool vs PU, With the Numbers

Two panels with the same steel skin and the same thickness can differ in price by more than half, and in fire behaviour by an entire class. The core decides both.

02 Nov 2026Technical Guide

Buyers ask for sandwich panels constantly and quote them rarely, because a panel is sold by the square metre and the core is buried inside. Two quotations for the same building can therefore describe completely different products — and the cheaper one is not automatically the better one.

Why the sandwich panel core decides your price, your insulation and your fire rating

A sandwich panel is two steel skins bonded to an insulating core. The skins carry the weather and the finish. The core insulates, holds the skins apart against wind suction, takes the compressive load between them, and decides how the panel behaves in a fire.

Cost follows from the same place. Foam cores are light and cheap per cubic metre; mineral wool cores are heavy and dearer. Since a panel is priced by area, the price gap between cores is decided by how much core each square metre needs — which is why thickness and core must be judged together.

Sandwich panel continuous compounding line - foam core panel production machine

We run a continuous sandwich panel line in Foshan producing EPS, rock wool, glass wool and PU cores from 50 mm to 200 mm.

Sandwich panel core comparison: the five cores at a glance

Thermal conductivity decides insulation. Density decides how heavy the panel is and how much load it puts on your frame. Fire behaviour decides if the panel is permitted.

Sandwich panel core comparison — the five cores in commercial use
Core	Thermal conductivity λ (W/m·K)	Density (kg/m³)	Fire behaviour (EN 13501-1)	Water and joint behaviour
EPS	0.035 – 0.040	15 – 25	E to B2 — combustible unless treated	Closed cell; light, easy to cut
Rock wool	0.040 – 0.044	100 – 120	A2-s1,d0 — non-combustible	Porous; joints must be sealed
Glass wool	0.032 – 0.036	24 – 48	A1 / A2 — non-combustible	Porous, light; excellent acoustics
PU	0.022 – 0.026	38 – 42	B-s2,d0 typically	Closed cell; stable, moisture resistant
PIR	0.021 – 0.024	40 – 45	B-s1,d0 typically — chars, slows flame	Closed cell; fire-enhanced PU alternative

Indicative reference ranges for typical commercial panels. A fire classification belongs to the tested panel, not to the name of the foam — always request the test report for the product you buy.

Thermal performance by sandwich panel core: U-value and weight

Compare the U-value, not the thickness: this is the fastest way to see why two quotations can be priced differently and both be honest.

Indicative U-value (W/m²K) and panel weight (kg/m²) by core and thickness
Core	50 mm	75 mm	100 mm	150 mm
EPS	0.64 / 7.0	0.44 / 7.4	0.34 / 7.8	0.23 / 8.5
PU	0.41 / 8.3	0.28 / 9.3	0.21 / 10.3	0.14 / 12.3
Rock wool	0.74 / 11.8	0.51 / 14.5	0.39 / 17.3	0.27 / 22.8

Each cell reads U-value / weight, for typical panels with 0.4 mm steel skins; U-values exclude joint and fixing effects. Note that 50 mm of PU insulates better than 75 mm of EPS. Final thickness and fixing must be confirmed by a structural engineer against your actual loads.

Which sandwich panel core should you specify for your building?

Start from the use of the space and the temperature you must hold inside, then work back to the core.

Core and thickness by application
Application	Core to specify	Typical thickness	Reason
Unconditioned warehouse, budget	EPS	50 mm	Lowest cost, lightest
Air-conditioned warehouse or factory	PU or PIR	75 – 100 mm	Controls the cooling load
Chiller or freezer room, +8 °C to −25 °C	PU or PIR	75 – 150 mm	Best U-value per mm
Blast freezer, cold store	PU or PIR	up to 200 mm	Highest insulation duty
Fire-rated wall, fire zone separation	Rock wool	80 – 150 mm	A2 core; 60 to 120 min tested
Generator or electrical room	Rock wool	80 – 150 mm	Non-combustible
Workshop roof, noise next door	Glass wool or rock wool	75 – 100 mm	Best sound insulation
Site office, annex, guard room	PU	50 – 75 mm	Light, no heavy frame

Two rules survive every project. Do not use EPS in a freezer — it has no useful performance at low temperature and the fire class is the wrong way to be. And do not switch core between roof and wall without checking the fixing, because rock wool is roughly 50 % heavier than PU of the same thickness.

Fire rating and what the sandwich panel core classification does not tell you

Rock wool and glass wool are non-combustible mineral fibres; their panels are typically A2-s1,d0 and A1, and tested wall systems can give 60 or 120 minutes of fire resistance depending on thickness. PU foam is combustible, but at B-s2,d0 it is self-extinguishing. PIR is the fire-enhanced version of PU: under flame the core chars, and that char slows flame spread.

One warning saves money: a classification belongs to the tested product, not to the name printed on a quotation. Ask for the fire test certificate for the exact panel — core, thickness, skins and joint system together — and check whether your code requires a specific class.

Roof panel span and purlin support by sandwich panel core thickness

For a self-supporting insulated roof panel, the panel spans between purlins, so the purlin spacing has to match the panel thickness and the load case. Thicker panels carry more load before deflecting, so they sit on wider spacing.

Indicative single span of a self-supporting insulated roof panel
Panel thickness	Indicative span between supports	Note
40 mm	≈ 3.0 m	Minimum practical roof thickness
60 mm	≈ 3.8 m	Common on unconditioned buildings
100 mm	≈ 4.8 m	Standard for insulated roofs
120 mm	≈ 5.0 m	Upper end of standard roof panels

Indicative only, for standard profiles and normal uplift. The permitted span must be taken from the panel manufacturer’s load table for your site wind and deflection limit, and the final purlin spacing verified by a structural engineer. Standard purlin spacing is 1.2–1.5 m.

Frequently asked questions

PU or PIR. They give the best U-value per millimetre, resist moisture and stay stable at low temperature. Use 75–100 mm for chiller rooms, 120–150 mm for freezers down to −25 °C, and up to 200 mm for blast freezing.

EPS is a combustible foam, classified E to B2 unless treated, so it is not appropriate where a fire-rated wall is required. It suits unconditioned warehouses and site accommodation. Where fire matters, specify rock wool or PIR.

Within one core, yes. Across cores, no: a 50 mm PU panel has a U-value of about 0.41 W/m²K while a 75 mm EPS panel is about 0.44. Compare U-values, not thickness, and ask any supplier for theirs.

75–100 mm of PU or PIR is the usual starting point, then adjust for your climate, roof orientation and the running cost you will carry. The roof is usually the bigger heat load, so spend the thickness budget there first.

Yes, and it is common — PU or PIR on the roof, EPS on unconditioned walls, rock wool on fire-rated walls, PU in the cold room. Check the purlin spacing and fixings for the heaviest core on that run.

Send the panel specification, get a comparable quotation

Tell us the areas, core, thickness, joint system and delivery point — or just the building size and use, and we will propose the core and thickness with the U-values and weights alongside the price. Reply within 24 hours.

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