Insulated Plasterboard

What Is Insulated Plasterboard?

Insulated plasterboard, sometimes called thermal laminate or insulated dry-lining, is a factory-bonded composite that pairs a sheet of gypsum plasterboard with a backing layer of insulation. 

By combining lining and insulation in a single panel, it delivers a finished internal surface and a thermal upgrade in one hit, saving space and installation time compared with fixing the two elements separately.

Board Edge Types: Tapered vs. Square

Tapered Edge

• What it is: The tapered edges create a shallow recess when two boards meet, leaving space for joint tape and compound to sit below the surface. Once filled and sanded, it creates a smooth, level finish across the joint.
• Benefits: Less drying time, minimal wet trades, and faster turnaround - great when you're planning to paint directly onto the boards.
• Installation tip: If you cut tapered boards to length, the new edge will be square. Try to place these cuts in corners or reinforce them with back-blocking tape to keep your joints looking seamless.

Square Edge

• What it is: The board’s thickness stays the same across all edges - no tapering.
• Finishing approach: These usually need a full skim coat of finishing plaster (often at least 2 mm thick) or a textured finish to hide any joins. That thickness can vary depending on how perfect you want the surface or how uneven the background is.
• Best for: Areas where the surface will be skimmed, tiled, or hidden such as behind wall cladding or built-in units.

Types of Gypsum Plasterboard Facing

• Type A - Standard: Suitable for most internal dry applications. No additional properties beyond standard strength and finish.
• Type F - Fire-Resistant: Reinforced with non-combustible fibres. Provides improved fire resistance and is typically specified for use in rated assemblies.
• Type H1/H2 - Moisture-Resistant: Contains additives that limit moisture uptake. Required in locations prone to damp or condensation.
• Type D - High-Density / Acoustic: Manufactured with increased density for improved sound insulation. Reduces airborne noise transmission between rooms.
• Foil-Backed: Comes with a factory-applied foil layer. Functions as an integrated vapour control layer in cold climates or retrofit situations.

Insulation Core Types

The insulation core is critical for thermal performance. Different materials offer varying properties:

Expanded Polystyrene (EPS)

• Thermal conductivity (W/m·K): 0.034-0.038
• Strengths: Low cost, easy to cut, recyclable.
• Considerations: Achieving desired insulation levels may require thicker panels; the material's softer surface is susceptible to dents or marks if adhesive points are too spread out.

Extruded Polystyrene (XPS)

• Thermal conductivity: 0.031-0.033
• Strengths: Higher compressive strength, closed-cell (water-resistant). 
• Considerations: Can contribute more to overall wall depth than PIR. 

Polyisocyanurate (PIR)

• Thermal conductivity (W/m·K): 0.022-0.024
• Strengths: Excellent thermal resistance per mm; foil facer often functions as VCL.
• Considerations: When used in certain building types or at specific heights, it must be paired with Type F gypsum to comply with relevant national or regional fire regulations.

Phenolic Foam

• Thermal conductivity (W/m·K): 0.019-0.021
• Strengths: Phenolic boards offer the best thermal conductivity among common foams; forms a protective char layer in fire.
• Considerations: Brittle edges require clean cuts; slightly higher cost than PIR.

Fixing Methods for Insulated Plasterboard

There are two main ways to fix insulated plasterboard, depending on the type of wall and the project requirements.

Dot and Dab (Adhesive Fixing):
The dot and dab method is often used on solid masonry walls. Adhesive is applied to the back of the board in spaced-out blobs (or "dabs"), allowing the board to be pressed directly onto the wall.

It’s a practical way to deal with uneven surfaces, especially in older properties. A continuous bead of adhesive around the edges helps seal the board, and a zigzag pattern through the centre adds strength.

To ensure it stays secure over time, mechanical fixings (screws) are sometimes added as extra support while the adhesive sets. Good bonding is key - gaps behind the board can affect insulation performance.

Mechanical Fixing to Battens or Studwork:
In stud wall builds, whether timber or metal, boards are screwed directly into place on the framework. This creates a space behind the board, which is useful for running cables or pipework.

If soundproofing is needed, acoustic insulation can go into this gap. Fire protection rules mean fire stops should be included at the top, bottom, and around any openings in the wall system.

The quality of the final result (no matter which fixing approach is used) comes down to good prep work. A clean, dry surface and accurate board placement are key to both efficiency and a neat finish.

It’s always best to follow the product instructions closely, especially when it comes to adhesive placement and how far apart fixings should be.

Thicknesses

We refer to all insulated plasterboards by their overall thickness, as this helps you to calculate how much space the board will take up.

For instance, Celotex has an insulated plasterboard product called "Celotex PL4025”, where the “25” refers to the fact that the thickness of the insulation board is 25mm. 

However, this is bonded to a 12.5mm plasterboard, making the overall thickness 37.5mm. We, therefore, call this product “37.5mm Celotex PL4025”.

All of the thicknesses listed on our site refer to the thickness of the insulation plus the plasterboard.