Insulation·glass wool 20mm
glass wool · 20mm
R 0.54
U 1.407 W/m²·K

glass wool, 20 mm — R 0.54

20 mm divided by a conductivity of 0.037 gives an R-value of 0.54. The U-value is 1.407, so a square metre leaks 28.15 W across a 20-degree difference.

Standards it meets

Not up to any of them yet

Material
glass wool
Thickness
20 mm
Thermal conductivity
0.037 W/m·K
Thermal resistance
0.54 m²·K/W
U-value
1.407 W/m²·K
Heat lost per square metre
28.15 W
As concrete
0.86 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 panel4 mm
  • phenolic foam11 mm
  • rigid polyurethane12 mm
  • extruded polystyrene15 mm
  • graphite EPS17 mm
  • white EPS19 mm
  • mineral wool22 mm
  • cellulose23 mm
  • timber70 mm
  • plasterboard97 mm
  • concrete865 mm

Nearby cells

glass wool 10mm
R 0.27
glass wool 30mm
R 0.81
white EPS 20mm
R 0.56
mineral wool 20mm
R 0.5

Same material, other thicknesses

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

Same thickness, other materials

vacuum panel 20mm
R 2.86
phenolic foam 20mm
R 1
rigid polyurethane 20mm
R 0.87
extruded polystyrene 20mm
R 0.71
graphite EPS 20mm
R 0.65
white EPS 20mm
R 0.56
glass wool 20mm
R 0.54
mineral wool 20mm
R 0.5
cellulose 20mm
R 0.48
timber 20mm
R 0.15
plasterboard 20mm
R 0.11
concrete 20mm
R 0.01

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 20 mm of glass wool?

0.54 — 20 mm in metres divided by a conductivity of 0.037.

Q. And the U-value?

1.407. That is 0.71 — the resistance plus 0.17 of surface — turned upside down, and a square metre leaks 28.15 W across 20 degrees.

Q. How much concrete would match it?

0.86 metres.

Q. Which standards does it meet?

At 1.407 it does not clear any of them yet.