Soprema PIR boards

Who makes Soprema PIR insulation boards

Soprema is a French manufacturer of waterproofing and insulation products, founded in Strasbourg in 1908. It began as a maker of bitumen-based roofing compounds and has grown into an independent, family-owned group with its head office still in Strasbourg, more than 11,000 employees and operations in over 90 countries. The current chairman is the third generation of the founding family to run the business, which helps explain its long-term approach to quality and investment.

The group has manufactured and sold PIR insulation across mainland Europe for years. Its reputation on site is for consistent boards, straightforward technical support and dependable supply, and its PIR boards are specified on everything from housebuilding to large commercial roofs. For a buyer in the UK, the Soprema name on a pallet means a product made by a group that has worked on the building envelope for well over a century.

Soprema in the UK

Soprema moved into UK PIR manufacturing in a big way in 2024, when it completed the purchase of a 75 per cent stake in Celotex, the Suffolk-based PIR business previously owned by Saint-Gobain, with Saint-Gobain keeping a 25 per cent minority holding for a transition period. The deal brought two established PIR factories into the group, at Hadleigh in Suffolk and Eggborough in Yorkshire. From January 2026 the Celotex range has been moving across to the Soprema name, so the general purpose board sold under that branding today comes off those same UK production lines.

Soprema UK runs from a head office at Witham in Essex. The practical result for anyone buying Soprema PIR insulation boards is a product that is made in Britain, supported in Britain and backed by a group with deep PIR manufacturing experience across Europe.

The general purpose Soprema PIR board

The board PIR Boards sells is Soprema's general purpose PIR board in the standard 2400 x 1200mm sheet, which covers 2.88 square metres. It has a rigid polyisocyanurate foam core with a low emissivity aluminium foil facing bonded to both sides. The declared thermal conductivity is 0.022 W/mK, and the board is available in every thickness from 20mm to 200mm, including the common 25mm, 50mm, 75mm, 100mm, 120mm and 150mm sizes.

The UK boards carry BBA Agrément certification, the independent assessment that building control officers, warranty inspectors and architects expect to see for pitched roof, wall and floor insulation. The manufacturing operation is run under ISO 9001 quality management and ISO 14001 environmental management systems, and the boards are UKCA marked for sale in Great Britain.

The board is called general purpose because it suits so many positions in a building with no change in performance. The foil facing does two jobs: it becomes a vapour control layer once the joints are taped, and it reflects radiant heat back into the room when it faces an unventilated air gap on the warm side.

Why 0.022 W/mK matters for your U-value

Thermal conductivity, written as lambda, tells you how much heat passes through a metre of material for each degree of temperature difference. The lower the figure, the better the insulation. At 0.022 W/mK, Soprema PIR insulation boards sit at the top end of rigid insulation boards, and PIR of this grade typically reaches a given U-value in roughly half the thickness of mineral wool.

The U-value you need is set by the Building Regulations or by your designer. To calculate it, divide the board thickness in metres by the lambda value to get its thermal resistance (100mm of PIR at 0.022 gives 0.1 divided by 0.022, or 4.55 m2K/W), add the resistances of the other layers in the build-up, then divide 1 by the total. Because every brand PIR Boards supplies is made to 0.022 W/mK, the calculation gives the same answer whichever one arrives, which is why your U-value does not change when the brand does.

Where Soprema PIR insulation boards are used

Soprema PIR insulation boards are used in almost every part of a domestic or light commercial build, and the thickness follows the position.

Pitched roofs: 100mm to 150mm cut to fit tightly between the rafters, often with 25mm to 50mm fixed across the underside to deal with the thermal bridge through the timber. Loft conversions follow the same pattern, with the thinner under-rafter layer helping to protect headroom.

Flat roofs: 100mm to 200mm laid above the deck in a warm roof build-up, or between the joists in older cold roof designs.

Floors: 75mm to 150mm laid over the concrete slab or between joists before the chipboard or screed goes down. Where there is underfloor heating, PIR board is the usual choice because it drives heat up into the room rather than down into the ground.

Timber frame and masonry walls: 50mm to 100mm between the studs, as a partial fill cavity board, or fixed to the inside of a solid wall before the plasterboard goes on.

Extensions and garden rooms: a mixture of the above, typically 100mm to 150mm in the roof and floor and 50mm to 100mm in the walls. The thin 20mm to 40mm boards are used for thermal breaks, lining window reveals, dormer cheeks and topping up where a few extra millimetres tip a U-value calculation the right way.

How PIR Boards supplies Soprema PIR insulation boards

PIR Boards sells by thickness rather than by brand. Soprema is one of the manufacturers we supply, and when you order a 100mm general purpose PIR board we send whichever of our supplied brands is best stocked for your postcode. That might be Soprema, or it might be another manufacturer making the same 2400 x 1200mm foil faced board to the same 0.022 W/mK specification.

We work this way for the customer's benefit. Every brand we supply meets the same thermal specification, so the U-value you calculated is unaffected. Drawing stock from more than one factory means we are rarely waiting for a single production line to catch up, which keeps lead times short and lets us hold trade prices down. Order before 2:30pm on a working day for delivery in 3 working days on average; dates can vary by area and availability. Delivery is free on UK mainland orders over £450 + VAT.

If a specification or warranty names Soprema PIR insulation boards, talk to us before you order so we can tell you what is realistic for your area. We would rather be straight with you than promise a brand we cannot guarantee.

Working out how many boards you need

Each 2400 x 1200mm PIR board covers 2.88 square metres. Measure the area to be insulated, divide by 2.88 and round up to the next whole board, then add about 10 per cent for cuts, offcuts too small to reuse and the odd damaged edge. For a pitched roof, measure the slope length rather than the horizontal span.

As an example, a 6m x 4m extension floor is 24 square metres. 24 divided by 2.88 is 8.3, so 9 boards, and adding 10 per cent takes you to 10 boards. Keep each element of the build to one thickness so the finished surface is level, and add up the roof, floor and wall totals before ordering so the whole job arrives in one delivery.

Cutting, fitting, taping and storing PIR board

PIR board cuts cleanly with a fine-toothed handsaw, a long-bladed insulation saw or a sharp knife for the thinner sheets. Measure the opening, cut the board a few millimetres oversize and press it into place so it grips between the rafters, studs or joists. Fill any remaining gaps with expanding foam and trim it flush once it has cured.

Tape every joint on the warm side with a foil insulation tape. Taped foil joints turn the individual boards into a continuous vapour control layer and stop moist air reaching the cold structure behind. Where a second layer runs under the rafters, stagger its joints against the first layer so nothing lines up.

Store the boards flat, on a level surface and off the ground, under cover or sheeted against rain. Keep the packaging on until you need them and avoid standing them on edge against a wall for long, because thinner boards will bow.