Does a lower-λ plasterboard make a warmer wall?

Only marginally. Plasterboard’s λ is high compared with insulation, and a board is thin, so its thermal resistance is small. The wall’s warmth is set by its insulation layer, not by the choice of board.

What is the difference between λ and R-value?

λ (W/mK) is a property of the material. R-value (m²K/W) is a property of a layer of given thickness — R = thickness ÷ λ — and it is what you add up across a build-up to reach a U-value.

When should I use a thermal laminate instead of standard board?

When the lining itself has to contribute insulation — for example dry-lining a solid wall. Thermal laminates bond an insulant to the board, are marked to EN 13950, and declare a whole-laminate R-value.

Thermal conductivity (λ) of plasterboard

What is the λ value on a plasterboard data sheet?

Thermal conductivity λ (W/mK) — how easily heat passes through the board. Lower values conduct less heat, i.e. insulate better.

λ (lambda) is a material property: how readily heat passes through the substance of the board, independent of how thick the board is. It is the starting point for any thermal calculation, but on its own it tells you that plasterboard is a lining, not an insulant.

Typical values, and what they imply

UK plasterboards typically declare a λ between about 0.19 and 0.25 W/mK. Denser acoustic and fire cores conduct slightly more heat than a standard core, so the higher end tends to belong to the heavier boards.

For comparison, a dedicated insulation product is an order of magnitude lower — mineral wool and rigid foams sit around 0.02–0.04 W/mK. That contrast is the point: a sheet of plasterboard adds negligible insulation, and choosing one board over another changes a wall’s U-value very little.

From λ to R-value and U-value

The insulating effect of a layer is its thermal resistance, R = thickness ÷ λ (in m²K/W). Because plasterboard is thin and its λ is relatively high, a single board’s R is small. Add up the R-values of every layer in a wall, take the reciprocal with the surface resistances, and you get the U-value — the whole element’s heat-loss rate.

So the board’s λ is a genuine input to a U-value calculation, but it is rarely the input that decides whether a wall meets its target.

When insulation is the job: thermal laminates

Where a lining genuinely has to insulate, the answer is a thermal laminate: a plasterboard bonded to an insulant such as EPS, PIR or XPS. These are made and marked to EN 13950, not EN 520, and they declare a whole-laminate thermal resistance (the board plus its insulant) rather than a board λ — which is the number that actually matters for insulation.

Reading the two correctly matters when substituting: a plain board’s λ and a laminate’s R-value are answering different questions, and one is not a proxy for the other.

Frequently asked questions

Does a lower-λ plasterboard make a warmer wall?: Only marginally. Plasterboard’s λ is high compared with insulation, and a board is thin, so its thermal resistance is small. The wall’s warmth is set by its insulation layer, not by the choice of board.
What is the difference between λ and R-value?: λ (W/mK) is a property of the material. R-value (m²K/W) is a property of a layer of given thickness — R = thickness ÷ λ — and it is what you add up across a build-up to reach a U-value.
When should I use a thermal laminate instead of standard board?: When the lining itself has to contribute insulation — for example dry-lining a solid wall. Thermal laminates bond an insulant to the board, are marked to EN 13950, and declare a whole-laminate R-value.

Related guides

Vapour-control (foil-backed) boards — What does a foil backing on plasterboard actually do?
EN 520 board types explained — What do EN 520 Type A, D, E, F, H, I, P and R mean?
Plasterboard weight: kg/m² and per board — How heavy is a plasterboard, and why do brands declare it differently?

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