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144 insulation cells — 100 mm of XPS equals 5.7 m of concrete

A thermal resistance and a U-value for every meeting of 12 materials and 12 thicknesses. Insulation cannot be described by the material alone or the thickness alone — one division settles it.

Conductivity is what a material is

Conductivity says how many watts pass through a square metre of a one-metre-thick slab per degree of difference. Lower is better. A vacuum panel is 0.007 and concrete is 1.6 — a factor of 230, and that factor turns straight into a difference in thickness.

Resistance is one division

Convert the thickness to metres and divide by the conductivity. For 100 mm of XPS that is 0.1 ÷ 0.028 = 3.57. Double the thickness and the resistance doubles, and resistances of stacked layers simply add — which is how a whole wall gets calculated.

The U-value is the other way up

A bigger resistance is better; the U-value is its reciprocal, so smaller is better there. Before flipping it, add the 0.13 and 0.04 that the air films on either face of the wall hold back — even a bare wall does that much. It is why zero thickness does not give an infinite U-value.

How many metres of concrete that is

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.

These figures are a starting point

Conductivity varies by product, and a real wall is several layers rather than one. Above all, a fastener, a window frame or a balcony slab becomes a thermal bridge that leaks past everything you calculated — the building is harder than the arithmetic.

Thermal conductivity

  • vacuum panel0.007 W/m·K
  • phenolic foam0.02 W/m·K
  • rigid polyurethane0.023 W/m·K
  • extruded polystyrene0.028 W/m·K
  • graphite EPS0.031 W/m·K
  • white EPS0.036 W/m·K
  • glass wool0.037 W/m·K
  • mineral wool0.04 W/m·K
  • cellulose0.042 W/m·K
  • timber0.13 W/m·K
  • plasterboard0.18 W/m·K
  • concrete1.6 W/m·K

Standards it meets

  • passive house 0.150.15 W/m²·K
  • Korean central-region wall 0.170.17 W/m²·K
  • loose standard 0.300.3 W/m²·K

Find it by material and thickness

Thermal resistance

vacuum panelλ 0.007 · As concrete 22.86m

vacuum panel 10mm
R 1.43
vacuum panel 20mm
R 2.86
vacuum panel 30mm
R 4.29
vacuum panel 50mm
R 7.14
vacuum panel 70mm
R 10
vacuum panel 100mm
R 14.29
vacuum panel 120mm
R 17.14
vacuum panel 150mm
R 21.43
vacuum panel 200mm
R 28.57
vacuum panel 250mm
R 35.71
vacuum panel 300mm
R 42.86
vacuum panel 400mm
R 57.14

phenolic foamλ 0.02 · As concrete 8m

phenolic foam 10mm
R 0.5
phenolic foam 20mm
R 1
phenolic foam 30mm
R 1.5
phenolic foam 50mm
R 2.5
phenolic foam 70mm
R 3.5
phenolic foam 100mm
R 5
phenolic foam 120mm
R 6
phenolic foam 150mm
R 7.5
phenolic foam 200mm
R 10
phenolic foam 250mm
R 12.5
phenolic foam 300mm
R 15
phenolic foam 400mm
R 20

rigid polyurethaneλ 0.023 · As concrete 6.96m

rigid polyurethane 10mm
R 0.43
rigid polyurethane 20mm
R 0.87
rigid polyurethane 30mm
R 1.3
rigid polyurethane 50mm
R 2.17
rigid polyurethane 70mm
R 3.04
rigid polyurethane 100mm
R 4.35
rigid polyurethane 120mm
R 5.22
rigid polyurethane 150mm
R 6.52
rigid polyurethane 200mm
R 8.7
rigid polyurethane 250mm
R 10.87
rigid polyurethane 300mm
R 13.04
rigid polyurethane 400mm
R 17.39

extruded polystyreneλ 0.028 · As concrete 5.71m

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

graphite EPSλ 0.031 · As concrete 5.16m

graphite EPS 10mm
R 0.32
graphite EPS 20mm
R 0.65
graphite EPS 30mm
R 0.97
graphite EPS 50mm
R 1.61
graphite EPS 70mm
R 2.26
graphite EPS 100mm
R 3.23
graphite EPS 120mm
R 3.87
graphite EPS 150mm
R 4.84
graphite EPS 200mm
R 6.45
graphite EPS 250mm
R 8.06
graphite EPS 300mm
R 9.68
graphite EPS 400mm
R 12.9

white EPSλ 0.036 · As concrete 4.44m

white EPS 10mm
R 0.28
white EPS 20mm
R 0.56
white EPS 30mm
R 0.83
white EPS 50mm
R 1.39
white EPS 70mm
R 1.94
white EPS 100mm
R 2.78
white EPS 120mm
R 3.33
white EPS 150mm
R 4.17
white EPS 200mm
R 5.56
white EPS 250mm
R 6.94
white EPS 300mm
R 8.33
white EPS 400mm
R 11.11

glass woolλ 0.037 · As concrete 4.32m

glass wool 10mm
R 0.27
glass wool 20mm
R 0.54
glass wool 30mm
R 0.81
glass wool 50mm
R 1.35
glass wool 70mm
R 1.89
glass wool 100mm
R 2.7
glass wool 120mm
R 3.24
glass wool 150mm
R 4.05
glass wool 200mm
R 5.41
glass wool 250mm
R 6.76
glass wool 300mm
R 8.11
glass wool 400mm
R 10.81

mineral woolλ 0.04 · As concrete 4m

mineral wool 10mm
R 0.25
mineral wool 20mm
R 0.5
mineral wool 30mm
R 0.75
mineral wool 50mm
R 1.25
mineral wool 70mm
R 1.75
mineral wool 100mm
R 2.5
mineral wool 120mm
R 3
mineral wool 150mm
R 3.75
mineral wool 200mm
R 5
mineral wool 250mm
R 6.25
mineral wool 300mm
R 7.5
mineral wool 400mm
R 10

celluloseλ 0.042 · As concrete 3.81m

cellulose 10mm
R 0.24
cellulose 20mm
R 0.48
cellulose 30mm
R 0.71
cellulose 50mm
R 1.19
cellulose 70mm
R 1.67
cellulose 100mm
R 2.38
cellulose 120mm
R 2.86
cellulose 150mm
R 3.57
cellulose 200mm
R 4.76
cellulose 250mm
R 5.95
cellulose 300mm
R 7.14
cellulose 400mm
R 9.52

timberλ 0.13 · As concrete 1.23m

timber 10mm
R 0.08
timber 20mm
R 0.15
timber 30mm
R 0.23
timber 50mm
R 0.38
timber 70mm
R 0.54
timber 100mm
R 0.77
timber 120mm
R 0.92
timber 150mm
R 1.15
timber 200mm
R 1.54
timber 250mm
R 1.92
timber 300mm
R 2.31
timber 400mm
R 3.08

plasterboardλ 0.18 · As concrete 0.89m

plasterboard 10mm
R 0.06
plasterboard 20mm
R 0.11
plasterboard 30mm
R 0.17
plasterboard 50mm
R 0.28
plasterboard 70mm
R 0.39
plasterboard 100mm
R 0.56
plasterboard 120mm
R 0.67
plasterboard 150mm
R 0.83
plasterboard 200mm
R 1.11
plasterboard 250mm
R 1.39
plasterboard 300mm
R 1.67
plasterboard 400mm
R 2.22

concreteλ 1.6 · As concrete 0.1m

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

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. How do I work out the R-value?

Divide the thickness in metres by the conductivity. For 100 mm of XPS: 0.1 ÷ 0.028 = 3.57.

Q. What is the difference between R and U?

The U-value adds 0.17 of surface resistance to the R-value and flips the total. Higher R is better; lower U is better.

Q. How much concrete equals 100 mm of insulation?

With XPS, 5.7 metres. The conductivities are 0.028 against 1.6, and that factor of 57 shows up as thickness.

Q. Does twice the thickness mean twice as warm?

The resistance doubles but the heat loss does not halve. The surface resistance is always there, so the first centimetres help far more than the last.

Q. Which standard should I aim for?

For an external wall, 0.17 in central Korea and 0.15 for a passive house. These figures cover one layer of insulation only; a real wall is the sum of its layers.