Insulation·extruded polystyrene 120mm
extruded polystyrene · 120mm
R 4.29
U 0.224 W/m²·K

extruded polystyrene, 120 mm — R 4.29

120 mm divided by a conductivity of 0.028 gives an R-value of 4.29. The U-value is 0.224, so a square metre leaks 4.49 W across a 20-degree difference.

Standards it meets

  • loose standard 0.30
Material
extruded polystyrene
Thickness
120 mm
Thermal conductivity
0.028 W/m·K
Thermal resistance
4.29 m²·K/W
U-value
0.224 W/m²·K
Heat lost per square metre
4.49 W
As concrete
6.86 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 panel30 mm
  • phenolic foam86 mm
  • rigid polyurethane99 mm
  • graphite EPS133 mm
  • white EPS154 mm
  • glass wool159 mm
  • mineral wool171 mm
  • cellulose180 mm
  • timber557 mm
  • plasterboard771 mm
  • concrete6857 mm

Nearby cells

extruded polystyrene 100mm
R 3.57
extruded polystyrene 150mm
R 5.36
rigid polyurethane 120mm
R 5.22
graphite EPS 120mm
R 3.87

Same material, other thicknesses

extruded polystyrene 10mm
R 0.36
extruded polystyrene 20mm
R 0.71
extruded polystyrene 30mm
R 1.07
extruded polystyrene 50mm
R 1.79
extruded polystyrene 70mm
R 2.5
extruded polystyrene 100mm
R 3.57
extruded polystyrene 120mm
R 4.29
extruded polystyrene 150mm
R 5.36
extruded polystyrene 200mm
R 7.14
extruded polystyrene 250mm
R 8.93
extruded polystyrene 300mm
R 10.71
extruded polystyrene 400mm
R 14.29

Same thickness, other materials

vacuum panel 120mm
R 17.14
phenolic foam 120mm
R 6
rigid polyurethane 120mm
R 5.22
extruded polystyrene 120mm
R 4.29
graphite EPS 120mm
R 3.87
white EPS 120mm
R 3.33
glass wool 120mm
R 3.24
mineral wool 120mm
R 3
cellulose 120mm
R 2.86
timber 120mm
R 0.92
plasterboard 120mm
R 0.67
concrete 120mm
R 0.08

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 120 mm of extruded polystyrene?

4.29 — 120 mm in metres divided by a conductivity of 0.028.

Q. And the U-value?

0.224. That is 4.46 — the resistance plus 0.17 of surface — turned upside down, and a square metre leaks 4.49 W across 20 degrees.

Q. How much concrete would match it?

6.86 metres.

Q. Which standards does it meet?

At 0.224 it clears 1 of them.