Heat Properties

Heat Properties
Thermal conductivity is the measurement of the speed at which heat travels through a material through conduction. In the United States thermal conductivity (also referred to as the "k" value) is commonly expressed in terms of the number of BTUs of heat which will travel through one sq. foot of material which is one inch thick when there is one degree F temperature difference across the material (ie. Delta T). This expression is often stated as btu/in/hr/sq.ft/oF. The lower the "k" value the better the thermal insulation. The term "R" value is frequently used to describe the performance of insulation materials. The "R" value is simply the reciprocal of the "k" value. Therefore, the higher the "R" value, the better the insulation quality.

For example: Polyurethane foam insulation board is commonly rated at a thermal conductivity of .17 (point one seven). This means that a 1" piece of foam 12" square would permit .17 BTUs of heat to move through it in one hour if there were a temperature difference of 10 F on either side. Were the temperature difference across the material to be increased to 10 degrees, then the 1.7 BTUs would move through it in the same hour.