Table of Contents
What Is Thermal Conductivity?
Thermal conductivity (k) measures a material's ability to conduct heat. It is the amount of heat transferred per unit time through a unit area with a unit temperature gradient. Materials with high k (metals like copper at 385 W/mK) transfer heat quickly, while insulators (fiberglass at 0.04 W/mK) resist heat flow. Understanding thermal conductivity is essential in building design, electronics cooling, and materials science.
The property depends on temperature and molecular structure. Metals conduct heat via free electrons, making them excellent conductors. Gases have low conductivity because molecules are far apart. Insulators trap air in small pockets to minimize convection and conduction.
Fourier's Law
Conductivity of Common Materials
| Material | k (W/mK) |
|---|---|
| Copper | 385 |
| Aluminum | 205 |
| Steel | 50 |
| Glass | 1.0 |
| Wood | 0.12 |
| Fiberglass | 0.04 |
| Air | 0.026 |
FAQ
What is R-value?
R-value is thermal resistance per unit area: R = L/k. Higher R means better insulation. US insulation uses imperial units (ft²·°F·h/BTU). Typical wall insulation has R-13 to R-21.
How does temperature affect k?
For metals, k generally decreases with temperature. For gases and insulators, k typically increases with temperature. For most engineering at moderate temperatures, room-temperature values suffice.