Thermal conductivity (k) describes how efficiently heat flows through a material. High k = good conductor; low k = good insulator.
Common Values (W/m·K)
- Copper: 401 — excellent heat conductor
- Aluminum: 237
- Steel: 50
- Glass: 1.0
- Wood: 0.12–0.17
- Fiberglass insulation: 0.04
- Air: 0.024
Fourier's Law
q = −k × A × (dT/dx), where q = heat transfer rate, A = cross-section area, dT/dx = temperature gradient.
Why Metal Feels Colder Than Wood at the Same Temperature
A metal countertop and a wood countertop in the same room are actually the same temperature, but metal's high thermal conductivity pulls heat away from your hand much faster than wood's low conductivity — your nerves sense the rate of heat loss, not the object's actual temperature, which is why metal always "feels" colder.
R-Value: The Inverse of Conductivity
Insulation is rated by R-value (thermal resistance), which is essentially the inverse of thermal conductivity — higher R-value means better insulation. R-value and thermal conductivity (k) relate by R = thickness / k, so a thicker layer of the same material always increases R-value proportionally.