Definitions of Common Heat Transfer and Insulation Terms

We know that K-factor is the rate at which heat flows through a material. It measures the heat in BTUs that passes through one square foot of a homogeneous substance, 1 inch thick, in an hour, for each degree F temperature difference and is expressed in BTU/ft2/F/hr./inch. The lower the K-value of a particular material the higher its insulating value.

Architects, engineers, and contractors use a number of these “factors” to express the insulation value of a material or a composite structure including “U,” ” C,” and “R.” The most common is the R-value, which is used in the building industry to rate the insulation properties of construction materials and building assemblies. Material suppliers often speak of products having a particular K-Factor, and industrial specifiers are familiar with the importance of the C-Factor, which is the rate of heat transfer through a material and is equal to the K-Factor when dividing the C-Factor by the thickness of the insulation.  For clarification, here is a page that provides definitions for the various “factors” that apply to heat transfer calculations.