R value

R value

  - Definition - the "resistance" of a substance to heat transfer by conduction (according to Energy, Its Use and the Environment)

The following information is obtained from Energy, Its Use and the Environment:

   "A measure of the resistance of the material to heat flow is the thermal resistance R, often called its "R-Value" given by R=delta over k.  The higher the R-value is, the bettwer are the insulating properties of the material. Using this notation, the rate of heat flow is given by 
           Qc/t = 1/R x A x change in T

R is a funciton of both the type of material and its thickness.