Thermal insulation — r-values と u-values

R-values と u-values for common building と industrial insulation materials.

thermalinsulationvalues

Overview

Thermal insulation reduces heat transfer between objects of different temperatures. The effectiveness is measured by:

R-value (thermal resistance) — higher is better:

$R = \frac{L}{k}$

where:

U-value (thermal transmittance) — lower is better:

$U = \frac{1}{R_{\text{total}}}$

The relationship: $U = 1/R$ and $R = 1/U$ .

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Thermal conductivity of common insulation materials
Insulation Material	Thermal Conductivity (k)(W/(m·K))	Density(kg/m³)	Max Temperature(°C)
Fiberglass batts	0.04	12	230
Mineral wool (rock wool)	0.038	40	750
Cellulose (blown)	0.04	45	80
Expanded polystyrene (EPS)	0.038	20	75
Extruded polystyrene (XPS)	0.034	35	75
Polyurethane foam (PUR)	0.025	35	110
Polyisocyanurate (PIR)	0.023	35	150
Phenolic foam	0.021	40	120
Calcium silicate	0.055	200	1000
Perlite	0.05	120	980
Ceramic fiber	0.06	128	1260
Aerogel blanket	0.015	150	650
Vacuum insulated panel (VIP)	0.007	200	60

出典: engineeringtoolbox.com

Insulation Thickness(mm)

Thermal Conductivity (k)(W/(m·K))

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出典: engineeringtoolbox.com

$R_{\text{SI}} \text{ (m^{2}·K/W)} = R_{\text{Imperial}} \text{ (ft^{2}·°F·h/Btu)} \times 0.1761$

Lower thermal conductivity means better insulation performance
Effective insulation requires continuous coverage — thermal bridges significantly reduce performance
Moisture reduces insulation effectiveness — vapor barriers are essential
Industrial pipe insulation typically requires minimum thickness calculations based on process temperature and ambient conditions