- Comparison between different insulators
- Three terms to know
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Mineral wool, vegetable or animal, expanded or extruded polystyrene, polyurethane foam: all these insulating materials have their advantages.

## Comparison between different insulators

Comparative table of thermal conductivity, thermal insulation, acoustic performance, moisture resistance and price between glass wool, rock wool, hemp wool, linen wool, wood fiber, sheep wool, duck feather, expanded polystyrene, extruded polystyrene and polyurethane foam.

## Three terms to know

### Thermal conductivity (λ)

Figured by the Greek lambda letter, thermal conductivity is the ability of a material to transmit heat (in W / m.K). The lower the lambda coefficient, the higher the insulating power of the material.**The lower the lambda coefficient, the more insulating the material.**

*Examples*:

• dry air: 0.024 W / m.K (very bad conductor)

• expanded polystyrene (density 11): 0.044 W / m.K

• rock wool, sheep, hemp, cellulose: 0.04 W / m.K

• extruded polystyrene (density 30): 0.035 W / m.K

• glass wool: 0.03 W / m.K

• polyurethane foam (density 35): 0.029 W / m.K

### Thermal resistance (R)

The thermal resistance (expressed in m².K / W) designates the capacity of a wall to oppose the passage of hot and cold. It depends on the thickness of the material and the lambda coefficient (R = thickness in meters / conductivity λ).**R = thickness / lambda**

The larger the R is, the more insulating the wall.

The larger the R is, the more insulating the wall.

*Examples:*

• rock wool 20 cm thick (lambda: 0.04), R = 0.2 / 0.04 = 5 m².° C / W

• 20 cm extruded polystyrene (lambda: 0.03), R = 0.2 / 0.03 = 6.6 m²° C / W (more effective)

• concrete wall 20 cm thick: R = 0.14

• 20 cm solid brick: R = 0.17

### The transmission coefficient (Up)

The surface transmittance of a wall (in W / m².K) corresponds to the amount of heat that passes through 1 m² of wall for a difference of 1° C between the two sides.**Up = 1 / R**

The higher Up is, the weaker the wall is.

The higher Up is, the weaker the wall is.

Example: a wall composed of 1.5 cm of plaster + 20 cm of hollow blocks + 8 cm of glass wool +1 cm of plasterboard displays an Up of 0.34 W / m².K.

Manufacturers generally aim to achieve an Up higher than 0.27 W / m2.K and up to a higher than 0.20 W / m2.K for comfortable labels.