PUF vs EPS sandwich panel: insulation, fire, moisture and when each fits

What is the difference between PUF and EPS panels?

PUF panel

A sandwich panel whose core is rigid polyurethane foam, foamed in place between the two steel skins so that it bonds to them as it cures. The closed cells hold a low-conductivity blowing gas, which is why PUF insulates so well for its thickness.

EPS panel

A sandwich panel whose core is expanded polystyrene (the white bead board sold as thermocol), cut into slabs and glued between the steel skins. The cells hold ordinary air, so EPS insulates less per millimetre than PUF.

From the outside both look the same: coated steel on both faces, the same profiles, the same joint types. The difference is inside, and it shows up in the thickness you need, how the panel behaves in fire and wet rooms, and the rate per square metre.

How much thicker does an EPS panel need to be?

Insulation is set by the core’s thermal conductivity (k) and thickness. With PUF at about 0.022 W/m·K and EPS at about 0.036 W/m·K (typical figures), EPS needs roughly 1.6 times the thickness to keep the same heat out.

In a cold room this matters twice. A thicker wall eats floor space inside a fixed footprint, and the extra heat through a thinner EPS wall runs the compressor harder every day. For a chiller or freezer, PUF at the right thickness for the temperature is usually the cheaper choice over the life of the room.

How do PUF and EPS behave in fire and in wet rooms?

Fire. Both cores are organic plastics and both burn; neither is non-combustible. EPS is a thermoplastic: it softens, shrinks back from the heat and can melt and drip, which may leave voids behind the steel. PUF is a thermoset: it chars rather than melts. Fire-retardant grades of each exist, and PIR (a modified polyurethane) chars further still. Where fire performance is the deciding factor, see PUF and PIR fire safety and consider mineral wool (rockwool) cores.

Moisture. Good PUF has a high closed-cell content and takes up little water. EPS also resists water, but the small gaps between its beads can let moisture creep in over years if the skins or joints are damaged. In both cases the steel skins and sealed joints do most of the work; cut edges and penetrations must be sealed.

Bond and strength. A foamed-in-place PUF core bonds to the skins over the whole face. EPS slabs rely on adhesive, so bond quality depends on the factory. For long roof spans and heavy walk-on loads, check the maker’s span table for the exact panel.

Is an EPS panel cheaper than a PUF panel?

Per square metre at the same thickness, yes: EPS is a cheaper core material and the panel is simpler to make. But the fair comparison is at the same insulation, not the same thickness. An EPS panel thick enough to match PUF uses more core, more transport volume and more floor space, which narrows or removes the gap.

Published per sq m rates for every PUF wall and roof thickness are on our price board, for example the 50 mm wall panel and the 100 mm wall panel (ex-works, GST and transport extra). EPS and rockwool options are described on the EPS and rockwool alternatives page.

When should you choose PUF and when EPS?

• Choose PUF for cold rooms, cold stores, freezers, ripening and mushroom rooms, and any room cooled below about +10 °C, where thickness and running cost decide.
• Choose PUF for roofs over people and heat-sensitive stock, where a thin panel must still keep heat out.
• EPS is often enough for ambient site offices, labour huts, partitions and temporary buildings where cost matters most and the room is not refrigerated.
• Consider rockwool or PIR where insurers, fire officers or the building code set a higher fire requirement than either standard core meets.

If you are unsure, send the room use, temperature and size with your enquiry; we will quote matched panels so the options can be compared on the same basis.