EPS vs mineral wool lambda

EPS and mineral wool can reach similar thermal targets, but they behave differently in walls, roofs, and floors. EPS is light, has widely available declared lambda values, and often works well where simple installation and some tolerance of occasional moisture are useful. Mineral wool is vapour open, non-combustible, and usually stronger acoustically, so it is often selected for ventilated facades, timber structures, and assemblies where fire resistance matters.

A useful comparison cannot stop at lambda. Thickness, fixings, board joints, compression, wind layers, render or cladding, and window details all affect the installed result. A small lambda advantage can be lost through thermal bridges, gaps, or interrupted insulation.

For example, 150 mm of EPS at lambda 0.036 W/mK gives roughly 4.17 m²K/W, while 150 mm of mineral wool at lambda 0.039 W/mK gives roughly 3.85 m²K/W. The difference is real, but the design decision should also consider moisture, fire behaviour, acoustic goals, system weight, and finish compatibility.

A common mistake is choosing only the lowest lambda or lowest price. In practice, complete system support, fixing quality, continuity at corners, and current manufacturer declarations matter more. If the result is close to a limit, compare several thicknesses and keep a reserve.

After comparing materials, move to the U-value calculator and test the complete assembly. The comparison table shows material differences, but the full build-up reveals the effect of render, cladding, air spaces, and surface resistances.

If two results are close, do not choose from one number alone. Check moisture behaviour, fire performance, available board formats, system requirements, and whether the layer can be installed continuously without open joints.

For renovation work, also check substrate condition, condensation risk, and details around windows, ring beams, and balconies. A strong lambda value will not fix a layer interrupted at the most important junctions.

The final step should be comparison with the current manufacturer data sheet. The database helps narrow the direction, but the documentation for the exact product matters most for ordering and construction.

In practice, make a short decision table: thermal result, installation difficulty, moisture behaviour, fire behaviour, acoustics, and system availability. That reduces the risk of choosing a material only because one number looks best.

If the comparison is used in a supplier discussion, record the data-check date and assumed thickness. It becomes easier to separate a price or product change from a real change in thermal performance.

A useful comparison includes at least three variants: current state, economical option, and option with margin. That shows whether extra thickness still delivers a meaningful improvement.

If the comparison is tied to legal requirements, do not rely on an internet average. Use the local threshold, the correct calculation method, and data for the product that will actually be installed.