Unilin PIR boards

Who makes Unilin PIR insulation boards

Unilin Insulation is the insulation division of the Unilin Group, a Belgian manufacturer headquartered at Wielsbeke in West Flanders. The group dates from 1960, when several families from the local flax industry started pressing flax waste into chipboard, and it has grown into a business with five divisions covering flooring, panels, insulation and related building products. Since 2005 the group has been part of Mohawk Industries, the American flooring group. When it rebranded its insulation business in 2023, the group reported more than 8,000 colleagues across 105 locations.

It describes its insulation arm as one of Europe's largest PIR insulation manufacturers, with plants in Belgium, France, Ireland and the UK. For the trade buyer, Unilin PIR insulation boards come with the consistency of a large, well-invested manufacturer.

From Xtratherm to Unilin Insulation

In the UK and Ireland, Unilin Insulation is the company that used to trade as Xtratherm. Xtratherm was founded in 1986 in Navan, County Meath, and built its reputation making foil faced PIR board for the Irish and British markets. The group bought the business in December 2015, and in 2021 it added Ballytherm, another Irish PIR maker, which brought a plant at Ballyconnell in County Cavan and a newly built factory at Ross-on-Wye in Herefordshire. From the start of 2023 the Xtratherm name was retired and the company became Unilin Insulation, with the same people, products and certificates behind it. Merchants still list the boards as Unilin, formerly Xtratherm.

Today the UK head office is in Chesterfield, Derbyshire, with UK manufacturing at Ross-on-Wye, while the Irish head office and the original factory remain in Navan. That footprint matters: Unilin PIR insulation boards sold in Britain are made in these islands rather than shipped across Europe, which keeps supply steady and lead times short.

The general purpose Unilin PIR board

PIR Boards sells Unilin's general purpose PIR board in the standard 2400 x 1200mm sheet, 2.88 square metres per board. It has a rigid polyisocyanurate foam core faced on both sides with aluminium foil and a declared thermal conductivity of 0.022 W/mK across the range. Thicknesses run from 20mm to 200mm, and we supply all of them, including the everyday 25mm, 50mm, 75mm, 100mm, 120mm and 150mm.

The general purpose board holds a BBA Agrément certificate for use in pitched roofs, floors and walls, which is the document building control and warranty providers will ask to see. The company operates certified ISO 9001 quality management, ISO 14001 environmental management and ISO 45001 health and safety management systems across its UK and Irish operations.

The board is called general purpose because it is not tied to one position in the building. The low emissivity foil on both faces gives a small extra performance gain where it faces an unventilated air gap, and once the joints are taped the foil doubles as the vapour control layer.

Why 0.022 W/mK matters for your U-value

Lambda, the thermal conductivity figure, is the starting point for every U-value. It describes how readily heat travels through a material, and a lower number means a better insulator. Unilin PIR insulation boards are rated at 0.022 W/mK, which puts them at the top end of the rigid board market and well ahead of mineral wool at around 0.035 to 0.044 W/mK. In practice you reach the same U-value with roughly half the thickness, which is why PIR insulation is the default choice where space is tight, such as a loft conversion or a flat roof upgrade.

To use the figure, convert the thickness to metres and divide by lambda. A 150mm board gives 0.15 divided by 0.022, or 6.82 m2K/W of thermal resistance; add the resistance of the plasterboard, air gaps and roof covering, then divide 1 by the total to get the U-value. Every brand PIR Boards supplies is made to 0.022 W/mK, so this sum does not change if a different brand turns up on the lorry.

Where Unilin PIR insulation boards are used

These boards go into the same places on a job as any premium PIR board, and the thickness you choose depends on the position.

In a pitched roof the usual approach is a thick board between the rafters, often 100mm or 120mm, with a thinner 25mm to 50mm layer across the face of the rafters to deal with the thermal bridge through the timber. Loft conversions tend to use the slimmest combination that meets the U-value so as to keep ceiling height.

In a warm flat roof the insulation sits above the deck and below the waterproofing, commonly 120mm to 200mm in one or two layers.

On the ground floor, 75mm to 150mm of PIR board goes above the slab or between the joists, and under a screeded underfloor heating system it stops heat soaking away into the ground.

In timber frame walls, 50mm to 100mm fits between the studs, and on solid masonry walls a similar thickness is fixed inside before the plasterboard. Extensions and garden rooms combine all of these, and customers often order 100mm or more for the roof and floor with 50mm for the walls. Thin boards from 20mm to 40mm are handy for thermal breaks, window reveals and dormer cheeks.

How PIR Boards supplies Unilin PIR insulation boards

We sell PIR by thickness, not by brand. Unilin is one of the manufacturers PIR Boards supplies, and when your order comes in we pick whichever of our supplied brands is best stocked for your postcode. Sometimes that will be Unilin, sometimes another maker of the same 2400 x 1200mm foil faced general purpose board at 0.022 W/mK.

This is deliberate and it works in your favour. Because every brand we supply is made to the same thermal specification, your U-value is unchanged. Because we draw on several factories, we are not stuck waiting for one of them to clear a backlog, so lead times stay short and we can keep trade prices low. Our delivery promise: 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 names Unilin PIR insulation boards, get in touch before ordering so we can tell you what is realistic for your postcode rather than promising something we cannot guarantee.

Working out how many boards you need

Divide the area you are insulating by 2.88, the coverage of one 2400 x 1200mm PIR board, and round up. Then add roughly 10 per cent for cutting waste. Measure roof slopes along the rafter, not across the plan.

A 5m x 5m garden room floor is 25 square metres: 25 divided by 2.88 is 8.7, so 9 boards, and 10 per cent on top makes 10. Do the same for the roof and the walls, keep each element to a single thickness, and add the totals together before you order so the whole job arrives in one drop rather than two.

Cutting, fitting, taping and storing PIR board

Cut PIR board with a fine-toothed saw or a long-bladed insulation knife, working on a flat surface with the foil face up to keep the edge tidy. For a friction fit between rafters or studs, cut 2mm to 3mm wider than the opening and push the board in square so it does not rock. Any gap you can see daylight through should be foamed and trimmed flush.

Tape the joints with foil tape on the warm side, pressing it firmly onto clean, dust-free foil. With two layers, run the second layer across the first so no joints line up.

Store the boards flat and dry, raised off wet ground and covered, with the manufacturer's wrapping intact until you use them. Avoid leaning full-size sheets against walls for days at a time, as the thinner sizes will bow, and strap or weight an opened pack because PIR is light enough to lift in a strong wind.