Celotex Insulation

Celotex is now Sopratherm

Celotex is now Sopratherm. Same product codes, same UK manufacturing and the same declared thermal performance. Stock currently held is Celotex-branded and remains fully valid for use. If you are ordering against a drawing that specifies Celotex, or matching boards to an existing build-up, nothing changes technically.

What the Soprema rebrand means for your order.

What is Celotex insulation?

Celotex insulation is a rigid polyisocyanurate (PIR) board with low emissivity composite aluminium foil facings, manufactured in the UK and supplied in 2400mm x 1200mm sheets with a declared thermal conductivity of 0.022 W/mK. It is used in floors, walls, pitched roofs and loft conversions to meet Building Regulations U-value targets. The brand is now Sopratherm, owned by Soprema, with product codes and performance unchanged.

The range splits into two product types. Celotex PIR insulation boards are the rigid foil-faced boards, sold in the TB4000, GA4000 and XR4000 ranges. Celotex insulated plasterboard, the PL4000 range, bonds the same PIR core to a sheet of plasterboard so a solid wall can be insulated and finished in one operation.

That 0.022 W/mK figure is why a Celotex board reaches a given U-value at a fraction of the depth a fibre-based product would need. The boards carry zero ozone depletion potential and low global warming potential, are light enough to handle single-handed, and cut cleanly on site with a fine-toothed saw or insulation knife.

Celotex insulation boards at a glance

Celotex PIR insulation boards

The rigid boards account for most Celotex sold. All three ranges share the same PIR core, the same foil facings and the same 0.022 W/mK lambda: what separates them is thickness and the job each thickness suits. All are supplied in 2400mm x 1200mm sheets and need overboarding or covering once fixed, since the board itself is not a finished surface.

Celotex TB4000 thermal break boards, 20mm to 40mm

TB4000 is the thermal break board in the Celotex range, supplied in 20mm, 25mm, 30mm and 40mm. TB stands for thermal bridging: the reveals, lintels, junctions and structural elements where cold spots and heat loss concentrate. These are the boards for narrow spaces, thin overboarding and multi-layer build-ups where depth is at a premium.

Celotex GA4000 general application boards, 50mm to 100mm

GA4000 is the general application PIR board, running from 50mm to 100mm in 10mm steps. It is most commonly used as internal wall insulation, and is equally at home in floors and pitched roofs. GA4100, the 100mm board, is the best selling thickness in the range.

Celotex XR4000 extra resistance boards, 110mm to 200mm

XR4000 is the extra resistance board, covering 110mm, 120mm, 125mm, 140mm, 150mm and 200mm. These are the thicknesses for jobs where depth is available and the U-value target is demanding, most often warm deck flat roofs and deep floor build-ups.

Celotex insulated plasterboard

Celotex insulated plasterboard, sold as the PL4000 range, is a different product to the rigid boards above. A PIR board with a paper facing is laminated to 12.5mm tapered edge plasterboard, giving insulation and a plaster-ready surface in a single fix. It is the standard approach to dry lining a solid wall, and it saves the separate battening and boarding stage that a rigid board requires.

Total thickness is the 12.5mm of plasterboard plus the PIR, which runs from 25mm to 60mm. All four boards are supplied at 2.4m x 1.2m, covering 2.88m² per board:

The thinner boards suit rooms where floor area matters more than the last fraction of a U-value; the thicker ones where the target is demanding and you can afford to lose the depth. Fixing is by dot and dab adhesive or mechanical fixings depending on the substrate and the specification. Joints are taped and filled as with standard plasterboard, and the tapered edge takes a skim or a jointed finish. Where a vapour control layer is required by the design, it must be installed separately: the board facing does not perform that role.

Celotex insulation by application

Celotex floor insulation

Floors take more Celotex than any other application, and the right board depends on the floor type.

Solid ground floors: Boards are laid over the slab under a screed or floating deck, or below the slab where the design calls for it. The damp proof membrane position relative to the insulation is set by the drawing, so check it before you lay anything. 100mm and 150mm are the thicknesses most often specified, with GA4000 covering the shallower build-ups and XR4000 taking over where the target U-value is demanding.

Suspended timber floors: Boards are cut to friction-fit between joists, supported on battens or clips, and finished flush with the joist tops. Where the joist depth allows, a continuous layer laid over the joists closes the thermal bridge across the timbers, which a between-joist fit alone leaves open.

Block and beam floors: Boards sit over the beams and blocks below the screed, with thickness driven by the U-value target rather than the structure.

Floating floors: Under chipboard or engineered flooring, the board needs to be laid tight and level: gaps show up as movement underfoot. 25mm to 50mm is typical where the finished floor level is fixed and depth is short.

Whichever the floor type, the thickness is a function of the U-value target and the depth available under finished floor level, not a fixed rule. Browse all floor insulation.

Celotex wall insulation

There are two routes. Fix rigid Celotex PIR insulation boards to battens or a stud frame and overboard with plasterboard, or use Celotex insulated plasterboard and combine both operations in one fix. The first gives more control over the build-up and suits framed walls; the second is faster on a solid wall and loses less room depth. Celotex is also used within timber frame and steel frame walls. Reaction-to-fire requirements govern what can be used in the external walls of buildings above 11m in height, so check the specification before ordering PIR for that application.

Celotex roof insulation

Used in pitched roofs between and under rafters, in warm deck flat roofs above the deck, and in cold deck build-ups. Rafter depth, ventilation strategy and the required U-value between them dictate the thickness. Where a full fill between rafters is not achievable, a thinner TB or GA board fixed under the rafters closes the bridge across the timbers. Browse all roof insulation.

Celotex loft insulation and loft conversions

Where a loft is being converted to living space rather than left cold, rigid PIR between and under the rafters brings the room inside the insulated envelope and preserves headroom in a way that a roll laid at joist level cannot. Boards can also be cut to fit tight between loft joists and finished flush, giving a firm, level base to lay loft boards over without crushing the insulation, which is what happens when boarding is laid straight onto a mineral wool roll.

Celotex thicknesses, sizes, R-values and U-values

Celotex boards are supplied in 2400mm x 1200mm sheets in a range of thicknesses.

Three thicknesses account for most orders: 50mm for stud walls and shallow floor build-ups, 100mm for standard floor and rafter work, and 150mm where the target U-value is demanding and depth is available.

Thermal resistance (the R-value) rises with thickness at a fixed lambda of 0.022 W/mK, and the declared figure for each board is listed on its product page. U-value is a different measure: it belongs to the whole construction rather than the board, so it depends on the substrate, cavity, fixings and finishes around the insulation. Two identical 100mm boards will give different U-values in different walls, which is why a single "100mm Celotex U-value" figure does not exist.

Celotex insulation prices

Prices vary by range and thickness: TB4000 boards are the lowest cost per sheet, GA4000 sits in the middle, and XR4000 and PL4000 carry the most material per board. Live pricing on every thickness is shown on the product pages above, with volume rates available on larger quantities and free delivery on orders over £500 ex VAT. Every board supplied is new, full-size and unblemished: Insulation UK does not sell seconds, offcuts or damaged stock, so what arrives on site is what you specified.

Why choose Insulation UK for Celotex insulation

• Full range stocked: Celotex PIR insulation boards in TB4000, GA4000 and XR4000, plus PL4000 insulated plasterboard, held in depth so mixed-thickness orders ship together.
• Trade pricing: Direct pricing on every thickness, with volume rates on larger quantities.
• Fast UK-wide delivery: Dispatched from Rotherham, with free delivery on orders over £500 ex VAT.
• Fifty years of industry experience: Advice from people who understand what goes into a build-up, not just what sits on the shelf.

Celotex insulation: common questions