Conduction

The molecule-to-molecule transfer of kinetic energy (on molecule becomes energized and, in, turn energizes adjacent molecules). A cast-iron skillet handle heats up because of conduction through the metal.

Convection

The transfer of heat by physically moving the molecules from one place to another. Hot air rises; heated water thermosiphons; our forced-air heating systems work by moving hot air from one place to another.

Emissivity

A measure of a surface's ability to emit long-wave infrared radiation of room temperature radiant heat energy. Emissivity varies from 0 (no emitted infrared) to 1 (100% emitted infrared). The lower the emissivity, the lower the resultant U-Value.

Extrude

To shape (a plastic, for instance) by forcing it through a die.

R Value

The R Value is a measure of the materials resistance to heat flow, expressed mathematically as 1/U Value.

Radiation

The transfer of heat through space via electromagnetic waves (radiant energy). A campfire can warm you even if there is a wind between you and the fire, because radiation is not affected by air.

Shading Coefficient

The ratio of solar heat gain through a glazing to the solar heat gain through a single lite of 1/8" (3mm) clear glass. The lower the number, the better the glazing is at preventing solar gain.

Solar Heat Gain Coefficient

The amount of solar radiation which enters a building as heat. The lower the number, the better the glazing is at preventing solar gain.

U Value

This represents the heat flow rate through a window expressed in BTU/hr/ft²/F using winter weather conditions of 0 degrees outside and 70 degrees inside. The smaller the number, the better the window system is at reducing heat loss.

UltraViolet Light Transmission

The amount of UltraViolet Light Transmission in the solar spectrum that is transmitted through a window which can cause fading. The lower the number, the better the window system is for reducing fading potential of carpets and interior furnishings.