37.5mm Celotex PL4025 is a two-in-one PIR insulated plasterboard, also known as a thermal laminate. It pairs a 25mm rigid polyisocyanurate (PIR) insulation core with a 12.5mm tapered edge plasterboard, bonded together to give an overall board thickness of 37.5mm. The PL4025 product code reflects this make-up, with the '25' denoting the 25mm PIR core (some buyers round the board up and call it 38mm insulated plasterboard, though the true thickness is 37.5mm). It is used to insulate and dry line internal walls and roof linings in a single operation, which is why it remains a common choice for upgrading the thermal performance of new build and refurbishment projects. Celotex is one of the most widely specified PIR brands in the UK, and PL4025 brings that insulation together with a ready-to-finish plasterboard face.

Each board measures 2400mm x 1200mm, covers 2.88m² and is supplied individually. The paper-faced PIR core delivers a thermal conductivity (lambda) of 0.022 W/mK, and the board carries an R-value (thermal resistance) of 1.20 m²K/W, measured including the plasterboard. At around 9.99 kg/m², the 37.5mm board is the slimmest and lightest in the PL4000 range, which makes it straightforward to handle and well suited to jobs where wall or ceiling depth is limited. Where a higher R-value is needed in the same build-up, the range steps up through 52.5mm, 62.5mm, 72.5mm and 77.5mm boards.

The plasterboard face has a tapered edge, so once the boards are butted together the joints can be taped with scrim and filled flush ready for decoration. Combining the insulation and the lining in one board removes a separate plasterboarding stage, cutting time on site and reducing the number of fixings and materials needed to reach a finished, insulated surface.

37.5mm Celotex PL4025 is specified for internal wall dry lining on solid masonry and timber frame walls, and as a lining beneath pitched roof rafters and flat roof joists. On internal walls it is direct-bonded to masonry with dot and dab adhesive or mechanically fixed to battens, and in roof applications it is fixed beneath the rafters or joists to form an insulated, ready-to-finish ceiling or sloping soffit. As the slimmest board in the range it suits reveals, modest thermal upgrades and rooms where floor area and headroom are tight, across both domestic and non-domestic refurbishment and new build. Install it in line with the latest Celotex technical guidance, the project specification and current Building Regulations, including fire requirements, any ventilation or air gap the build-up calls for, and the limit on external wall use. Fitted correctly, the board helps limit the risk of surface condensation on the internal face and supports lasting energy savings.

Key Benefits of Celotex PL4025:

• Two-in-one thermal laminate: a 25mm rigid polyisocyanurate (PIR) core bonded to 12.5mm tapered edge plasterboard, 37.5mm overall.
• Thermal conductivity of 0.022 W/mK, delivering strong thermal performance at the slimmest board depth in the range.
• R-value (thermal resistance) of 1.20 m²K/W, measured including the plasterboard.
• Insulates and dry lines in a single operation, cutting out a separate plasterboarding stage and reducing time and labour on site.
• Tapered edge plasterboard for taped, flush-filled joints and a ready-to-decorate finish.
• Fixes by mechanical fixing to battens or studwork, or by direct bonding (dot and dab) to masonry.
• The slimmest and lightest board in the PL4000 range, suited to window and door reveals and rooms where space is at a premium.
• Euroclass B-s1, d0 reaction-to-fire classification to BS EN 13501-1.
• BRE Green Guide A+ rating, which can support BREEAM credits.
• Manufactured with a blowing agent that has zero Ozone Depletion Potential (ODP) and low Global Warming Potential (GWP), and is CFC/HCFC free.
• BBA certified (Certificate 16/5357) for plasterboard thermal laminate applications, across new build and refurbishment.
• Supplied as a single 2400mm x 1200mm board covering 2.88m².

Good to know:

• Overall thickness of 37.5mm is made up of a 25mm rigid PIR core plus a 12.5mm tapered edge plasterboard.
• Butt the tapered edges tightly together, then tape the joints with scrim and fill flush before decorating.
• Fix mechanically to timber battens or studwork, or direct-bond to masonry with dot and dab adhesive.
• The bonded plasterboard face provides both the internal finish and the board's Euroclass B-s1, d0 reaction-to-fire performance, so no separate fire-rated lining is needed over it.
• Follow the latest Celotex guidance on vapour control for the application; some build-ups still need attention to interstitial condensation.
• Take care lifting and fitting full boards: the bonded plasterboard adds weight over a bare PIR board, at around 9.99 kg/m².
• Celotex PL4025 should not be used in the external walls of buildings over 11 metres in height; check current Building Regulations for your project.
• Store boards flat, off the ground, in their packaging and protected from the weather, keeping the plasterboard face dry.

As the slimmest board in the PL4000 range, 37.5mm Celotex PL4025 brings a thermal upgrade and a finished plaster surface together in one slim 37.5mm board, keeping internal walls, reveals and roof linings simple where floor area and headroom are at a premium.

If space is not the constraint, you can reach the same R-values for less outlay: we also stock Tekwarm HP+ Insulated Plasterboard, which balances energy efficiency against budget, alongside Tekwarm PIR Insulated Plasterboard as a like-for-like laminate alternative to Celotex PL4000. You can download the full Celotex PL4025 datasheet for the complete specification and installation detail.

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.