The polyisocyanurate (PIR) Insulation board is one of the most popular construction materials, primarily used for pitched roofs, walls, and floors in domestic and industrial projects.
We stock the most desirable brands, including Ecotherm, Recticel, and Kingspan PIR insulation. These boards are available in various thicknesses from 20mm to 150mm. They deliver an excellent thermal conductivity of 0.022 W/mK across all thicknesses and boast superb compressive strength.
PIR foam is made through a chemical reaction that results in a closed-cell structure that traps gas. Because blowing agent gas has lower thermal conductivity than air, it is among the most energy-efficient insulating materials on the market.
The material’s low thermal conductivity, combined with its ease of handling and versatility in a variety of applications, has made it increasingly popular among architects and contractors.
The boards do not work on their own, though. Each piece of PIR is wrapped in a facing – usually a foil, a glass-tissue layer, or a bitumen-ready coating – and those facers do as much work as the foam itself. They control moisture, help the board bond to membranes, stiffen the panel, and can influence aspects of fire performance.
PIR insulation is suited to diverse applications:
PIR insulation Polyisocyanurate can be grouped by application:
These are used on concrete, timber, or metal decks for warm roofs. Flat-roof PIR always needs facings that work with a membrane, so the facer type is a big deal here.
a) Bitumen-coated glass-tissue facer
b) Glass-tissue (mineral-coated) facer
c) Foil facer (less common for roofs)
These are used in loft conversions, attic refurbishments, warm pitched roofs, and dormer cheeks. They are moisture-tolerant, rigid, and easy to cut around rafters.
Foil-faced PIR (the standard)
For new-build cavity walls, partial-fill, or full-fill, depending on design. They resist moisture ingress, fit neatly between wall ties, and prevent thermal bridging.
a) Foil facers (highly reflective)
b) Textured/embossed foil
c) Water-repellent coated facers
For ground floors, suspended timber floors, and refurb work where weight and compressive strength matter. Floor PIR has high compressive strength, resists moisture, and keeps thermal performance stable beneath screed.
We stock a full range of PIR Polyisocyanurate boards from all the major brands – from everyday 25–150mm sheets right up to heavy-duty roof and floor specs, depending on the product.
We offer competitive PIR insulation prices for single boards, as well as wholesale, bulk, and trade discounts when you are loading up for a full job.
We provide fast dispatch, nationwide delivery, and dependable timescales.
You can buy PIR board insulation online from specialist insulation stores such as Insulation Wholesale. As a leading PIR insulation supplier, we stock a full range of panels for walls, floors, roofs, and lofts – from foil-faced wall panels to roof-ready boards and heavy-duty floor insulation. If you are budgeting for a project, our team can provide quick, accurate quotes so you know the current PIR insulation prices before you order.
Mark your cut line. Use a straightedge or long level. If your line is crooked, your cut will be too.
Score the foil first. Take a sharp utility knife and lightly score along your line. This does not slice the board – it just breaks the foil, leaving a neat edge.
Deepen the cut. Run your knife over the same line three or four times. You will feel it sink deeper each pass. For thinner boards (25–50mm), you can usually cut through the material with the knife alone.
Snap the board. For thicker boards (75–150mm), once the knife has cut through the foil and a bit into the foam, tilt the board over an edge or your knee and snap it along the scored part. The core breaks cleanly.
Trim the back. After snapping, the face will be clean-cut, and the back partially torn. Score the back foil with your knife and slice off the remaining foam.
Optional: use a handsaw. If you prefer one tool start to finish, a fine-tooth handsaw works well. It is slightly messier but great for deep cuts or angled pieces.
1.Between Studs, Joists, or Rafters
This is the classic “cut to fit and friction-fix” method.
Cut each board 3–5 mm wider than the gap.
Fit it into the space so it grips the sides. That slight pressure keeps it snug.
Make sure the face of the board sits flush with the timber so your plasterboard or internal lining lands cleanly.
Tape the foil joints to get a tighter vapour barrier.
PIR is rigid enough to bridge the gap, and the foil face helps stop air movement. Always follow system-specific guidance for vapour control and ventilation requirements.
2.Over Joists, Rafters, or Stud Walls (Continuous Layer)
This provides the best thermal performance by eliminating cold spots.
Fix the boards directly over the timber using insulation fixings or long screws with washers.
Stagger the joints so no straight lines run through the insulation.
Tape all joints with foil tape to seal the layer.
Fit your plasterboard or deck on top using long screws that reach the timber below.
The full sheet covers every timber, giving a more even thermal layer.
3.Solid Masonry Walls (Internal Facing)
This is the "insulated lining board" approach.
Dot-and-dab adhesive or mechanical fixings can be used, depending on the spec.
Boards must sit flat with no steps between them.
Tape joints, then add plasterboard over the top, or use insulated plasterboard that includes PIR.
It creates a warm internal surface and stops heat from bleeding into the cold wall.
4.Floors
Most PIR in floors is installed under the screed or under a chipboard deck.
Lay a DPM if needed.
Put PIR boards tightly together with staggered joints.
Tape where required, then add your screed or deck on top.
The rigid foam handles the load once it is supported by the layers above.
5.Flat Roofs
Both warm-roof and inverted-roof setups commonly use PIR.
Lay the boards over the roof deck.
Stagger joints.
Mechanically fix or bond, depending on the roof system.
Add the waterproofing membrane over the top.
PIR itself does not soak up water easily. So if the board gets a light splash or short-term exposure, it will not suddenly fall apart or lose its thermal performance. But it is not designed to stay wet because this can affect long-term stability. Long-term immersion or condensation behind the board can degrade facers or structure.
Yes, PIR insulation works very well in a loft.
Fit PIR panels snugly between the rafters, leaving the required ventilation gap above – usually 25–50mm, depending on the roof. Seal small gaps with foam or tape to prevent cold bridges.
A continuous layer of foil-faced PIR is fixed across the underside of the rafters. This adds thermal performance, covers up imperfect cuts between rafters, and the foil layer acts as a vapour-control layer once joints are taped.
If you are re-roofing, PIR slabs can be laid on top of the rafters before the breather membrane and tiles go on. This gives you a full warm roof with minimal thermal bridging – the most efficient loft system, but only practical during roof replacement.
100mm Celotex CW4100 Cavity Wall Insulation Board is an easy to install polyisocyanurate (PIR) insulation board with excellent thermal performance, featuring a low emissivity foil facing.
100mm Celotex GA4100 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
100mm Ecotherm Eco-Versal is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Ecotherm Eco-Versal is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
100mm Kingspan Thermaroof TR24 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. Kingspan Thermaroof is suitable for flat roofs waterproofed with partially bonded torch applied multi-layer bituminous waterproofing.
100mm Kingspan TR26 Thermaroof is high-performance insulation that has a fiber-free rigid thermoset polyisocyanurate (PIR) core. Suitable for flat roof application waterproofed with mechanically fixed single-ply waterproofing.
100mm Kingspan Thermaroof TR27 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. It is used to insulate flat roofs waterproofed with fully adhered single-ply, partially bonded built-up felt, mastic asphalt and cold liquid applied waterproofing.
100mm Recticel Eurothane GP is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Recticel is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
100mm Recticel Eurowall Partial Cavity is an advanced thermal insulation panel tailored for use in cavity wall systems, delivering exceptional energy efficiency and robust performance.
110mm Kingspan TR26 Thermaroof is high-performance insulation that has a fiber-free rigid thermoset polyisocyanurate (PIR) core. Suitable for flat roof application waterproofed with mechanically fixed single-ply waterproofing.
110mm Recticel Eurothane GP is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Recticel is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
110mm Unilin Thin-R PIR insulation is a foil faced, high-performance insulation solution that offers exceptional thermal efficiency and durability. This polyisocyanurate insulation board, formerly known as Xtratherm, is ideal for a range of applications, such as floors, pitched roofs, and walls.
115mm Recticel Eurowall Full Fill boards snap together with interlocking edges, forming a continuous thermal barrier that optimises performance of cavity wall insulation.
120mm Celotex XR4120 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
120mm Ecotherm Eco-Versal is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Ecotherm Eco-Versal is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
120mm Kingspan Thermaroof TR24 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. Kingspan Thermaroof is suitable for flat roofs waterproofed with partially bonded torch applied multi-layer bituminous waterproofing.
120mm Kingspan TR26 Thermaroof is high-performance insulation that has a fiber-free rigid thermoset polyisocyanurate (PIR) core. Suitable for flat roof application waterproofed with mechanically fixed single-ply waterproofing.
120mm Kingspan Thermaroof TR27 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. It is used to insulate flat roofs waterproofed with fully adhered single-ply, partially bonded built-up felt, mastic asphalt and cold liquid applied waterproofing.
120mm Recticel Eurothane GP is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Recticel is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
130mm Kingspan Thermaroof TR24 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. Kingspan Thermaroof is suitable for flat roofs waterproofed with partially bonded torch applied multi-layer bituminous waterproofing.
130mm Kingspan Thermaroof TR27 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. It is used to insulate flat roofs waterproofed with fully adhered single-ply, partially bonded built-up felt, mastic asphalt and cold liquid applied waterproofing.
140mm Celotex XR4140 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
140mm Kingspan TR26 Thermaroof is high-performance insulation that has a fiber-free rigid thermoset polyisocyanurate (PIR) core. Suitable for flat roof application waterproofed with mechanically fixed single-ply waterproofing.
140mm Kingspan Thermaroof TR27 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. It is used to insulate flat roofs waterproofed with fully adhered single-ply, partially bonded built-up felt, mastic asphalt and cold liquid applied waterproofing.
140mm Recticel Eurothane GP is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Recticel is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
140mm Recticel Eurowall Full Fill boards snap together with interlocking edges, forming a continuous thermal barrier that optimises performance of cavity wall insulation.
150mm Celotex XR4150 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
The 150mm Ecotherm Eco-Versal is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Ecotherm Eco-Versal is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
150mm Kingspan TR26 Thermaroof is high-performance insulation that has a fiber-free rigid thermoset polyisocyanurate (PIR) core. Suitable for flat roof application waterproofed with mechanically fixed single-ply waterproofing.
150mm Kingspan Thermaroof TR27 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. It is used to insulate flat roofs waterproofed with fully adhered single-ply, partially bonded built-up felt, mastic asphalt and cold liquid applied waterproofing.
150mm Recticel Eurothane GP is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Recticel is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
165mm XR4165 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
200mm XR4200 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
25mm + 12.5mm Celotex PL4025 PIR Insulated Plasterboard is it is suitable for use in roof and internal wall lining applications. Celotex Insulated Plasterboard is a high performance, easy to install PIR insulation board with a paper facing, laminated to a piece of 12.5mm tapered edge plasterboard.
25mm Celotex TB4025 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
25mm Kingspan TR26 Thermaroof is high-performance insulation that has a fiber-free rigid thermoset polyisocyanurate (PIR) core. Suitable for flat roof application waterproofed with mechanically fixed single-ply waterproofing.
25mm Kingspan Thermaroof TR27 is a high performance insulation with a fibre-free rigid thermoset polyisocyanurate (PIR) core. It is used to insulate flat roofs waterproofed with fully adhered single-ply, partially bonded built-up felt, mastic asphalt and cold liquid applied waterproofing.