200mm Celotex XR4200 is a rigid polyisocyanurate (PIR) insulation board and the range-topping thickness in the XR4000 line-up, the thickest PIR board Celotex supplies. It sits at the top of the range for one reason: where a floor or roof has to reach a very low, near-passive U-value, 200mm delivers it in a single board rather than a doubled build-up.

Each board measures 2400mm x 1200mm, covers 2.88m² and is sold individually. A declared thermal conductivity of 0.022 W/mK gives it a thermal resistance of 9.05 m²K/W, the highest single-board figure in the entire XR4000 range, at a maximum board weight of around 8.06 kg per square metre. The rigid PIR core is faced both sides with a low-emissivity aluminium foil that improves performance against a sealed cavity air space, and the square edges close up for a continuous, tight-jointed layer.

At 9.05 m²K/W a single 200mm board carries the resistance that thinner thicknesses can only reach by doubling up, so the most demanding target is met in one layer: one set of joints to tape, one plane of insulation, and no interface between two boards to detail.

XR4200 is specified as a single cut-to-fit layer in solid and suspended floors, in warm flat and pitched roofs between or under joists and rafters, and across masonry walls and timber- and steel-framed systems, typically on near-passive and high-performance projects where the U-value target sits at the strict end. Install it in line with the latest Celotex technical guidance, the project specification and current Building Regulations, including fire requirements and the height limit on external wall use. In wall build-ups it should be covered with a fire-rated lining such as 12.5mm plasterboard. As the thickest board in the range it is a special-order line, so allow additional lead time and confirm the build-up has the depth before specifying.

Key Benefits of 200mm Celotex XR4200:

200mm rigid polyisocyanurate (PIR) board, the range-topping thickness in the XR4000 line-up and the thickest PIR board Celotex supplies.
Thermal resistance (R-value) of 9.05 m²K/W, the highest single-board figure in the whole XR4000 range, for near-passive and high-performance targets.
Declared thermal conductivity of 0.022 W/mK, delivering that resistance in a single 200mm board.
Reaches a very low U-value in one layer that thinner boards would meet only by doubling up, cutting joints and board interfaces.
Used across solid and suspended floors, warm flat and pitched roofs, masonry walls and timber- and steel-framed systems.
Low-emissivity aluminium foil facings on both sides, improving performance against sealed and cavity air spaces.
Square edges for flush, tight joints and a continuous insulation layer.
Manufactured with a blowing agent of zero Ozone Depletion Potential (ODP) and low Global Warming Potential (GWP), free of CFCs and HCFCs.
Supplied as a single 2400mm x 1200mm board covering 2.88m², at a maximum board weight of around 8.06 kg per square metre.
BBA certified (Certificate 25/7318) for defined pitched roof, dry lining and floor applications.

Good to know:

Boards measure 2400mm x 1200mm and are sold individually, each covering 2.88m².
As the thickest board in the range, 200mm XR4200 is a special-order line: allow additional lead time when planning delivery.
The foil facing is printed on one side only: fit the board with the plain face towards the cavity for the rated thermal performance.
The foil facing is not a vapour control layer; many floor and roof build-ups still need a separate VCL to manage interstitial condensation.
In wall applications the board should be covered with a fire-rated lining, such as 12.5mm plasterboard.
Celotex XR4000 should not be used in the external walls of buildings over 11 metres in height; check current Building Regulations for your project.
PIR is moisture resistant but not waterproof: store boards flat, off the ground, dry and out of prolonged sunlight.
Insulation UK offers a bespoke cutting service, supplying boards cut to your sizes to reduce waste and on-site mess.

When the U-value target sits at the strict, near-passive end and the build-up has room for the full depth, 200mm Celotex XR4200 brings the range's highest single-board resistance to the floor or roof, doing in one layer what would otherwise take two.

Important Notice: Please be aware that during periods of high demand, we reserve the right to provide alternative brands that meet the same specifications and quality standards as the products you originally ordered.

200mm Loft Insulation