Insulation·concrete 400mm
concrete · 400mm
R 0.25
U 2.381 W/m²·K

concrete, 400 mm — R 0.25

400 mm divided by a conductivity of 1.6 gives an R-value of 0.25. The U-value is 2.381, so a square metre leaks 47.62 W across a 20-degree difference.

Standards it meets

Not up to any of them yet

Material
concrete
Thickness
400 mm
Thermal conductivity
1.6 W/m·K
Thermal resistance
0.25 m²·K/W
U-value
2.381 W/m²·K
Heat lost per square metre
47.62 W
As concrete
0.4 m

Thickness for the same performance

This is the number that shows what insulation is worth. Matching 100 mm of XPS with concrete alone would take 5.7 metres of it. No one builds a wall like that — which is why a concrete building only gets warm once a thin layer of insulation is added.

  • vacuum panel2 mm
  • phenolic foam5 mm
  • rigid polyurethane6 mm
  • extruded polystyrene7 mm
  • graphite EPS8 mm
  • white EPS9 mm
  • glass wool9 mm
  • mineral wool10 mm
  • cellulose11 mm
  • timber33 mm
  • plasterboard45 mm

Nearby cells

concrete 300mm
R 0.19
plasterboard 400mm
R 2.22

Same material, other thicknesses

concrete 10mm
R 0.01
concrete 20mm
R 0.01
concrete 30mm
R 0.02
concrete 50mm
R 0.03
concrete 70mm
R 0.04
concrete 100mm
R 0.06
concrete 120mm
R 0.08
concrete 150mm
R 0.09
concrete 200mm
R 0.13
concrete 250mm
R 0.16
concrete 300mm
R 0.19
concrete 400mm
R 0.25

Same thickness, other materials

vacuum panel 400mm
R 57.14
phenolic foam 400mm
R 20
rigid polyurethane 400mm
R 17.39
extruded polystyrene 400mm
R 14.29
graphite EPS 400mm
R 12.9
white EPS 400mm
R 11.11
glass wool 400mm
R 10.81
mineral wool 400mm
R 10
cellulose 400mm
R 9.52
timber 400mm
R 3.08
plasterboard 400mm
R 2.22
concrete 400mm
R 0.25

How to read this

  • Thermal resistance is the thickness in metres divided by the conductivity. Bigger is better.
  • The U-value adds 0.17 of surface resistance and then flips the total. Smaller is better.
  • Resistances add across layers, so a whole wall is the sum of its parts.
  • Conductivity varies by product; the values here are typical for the material.

Frequently asked questions

Q. What is the R-value of 400 mm of concrete?

0.25 — 400 mm in metres divided by a conductivity of 1.6.

Q. And the U-value?

2.381. That is 0.42 — the resistance plus 0.17 of surface — turned upside down, and a square metre leaks 47.62 W across 20 degrees.

Q. How much concrete would match it?

0.4 metres.

Q. Which standards does it meet?

At 2.381 it does not clear any of them yet.