Thermal resistance is the
temperature difference across a unit
area of a material of unit thickness when a unit of
heat energy flows through it in unit
time. It is the reciprocal of
thermal conductance. The units of thermal resistance are, in the
SI system,
K.
m²/
W. In the building trade, the traditional non-metric
R-value is sometimes used instead, with units
ft² °F.h/
Btu.
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