Thermal Insulation — R-Values and U-Values

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:

• $L$ = insulation thickness (m)
• $k$ = thermal conductivity (W/(m·K))

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

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

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

Insulation Material Properties

Typical R-Values for Building Assemblies

Unit Conversions

$R_{\text{SI}} \text{ (m²·K/W)} = R_{\text{Imperial}} \text{ (ft²·°F·h/Btu)} \times 0.1761$

Key Points

• 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

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