Thermal Conductivity

The thermal conductivity for various materials can be found in ASHRAE Handbook – Fundamentals. Thermal conductivity is a measure of how well a material conducts and promotes heat transfer. For example, metals are excellent conductors and thus have a high conductivity. Aluminum has a thermal conductivity of 128 Btu/(hr*ft*℉) and iron has a conductivity of ~30 Btu/(hr*ft*℉). Poor conductors include materials like wood (Douglas fir –0.0833 Btu/(hr*ft*℉)) and insulation materials (Cellular Glass - 0.0275 Btu/(hr*ft*℉) ; Glass Fiber – 0.0221Btu/(hr*ft*℉)).

It is important to note that often times, thermal conductivity is given in units of(Btu*in)/(hr*〖ft〗^2*℉),. This value is basically a thermal conductivity value per inch thickness of materials. Insulation, masonry, plastering and wood materials often have thermal conductivity per inch of materials. For example, cellular glass has a unit thermal conductivity of 0.33(Btu*in)/(hr*〖ft〗^2*℉)), which means that for an inch in thickness of cellular glass material the thermal conductivity is 0.33.

Besides thermal conductivity, materials can also be classified by their R-Value of their U-Factors as shown below.