${\bf BTU_{th}}$, Inch per Square Foot Hour Degree Fahrenheit, is an Imperial unit for 'Thermal Conductivity' expressed as $Btu-in/(h-ft^{2}-degF)$. A thermochemical British thermal unit inch per second per square foot per degree Fahrenheit is a unit of thermal conductivity in the US Customary Units and British Imperial Units. $1 Btu_{th} \cdot in/(h \cdot ft^{2} \cdot degF)$ shows that one thermochemical BTU of heat per one hour moves through one square foot of material, which is one foot thick due to a temperature difference of one degree Fahrenheit.
$Btu_{th} \cdot in/(h \cdot ft^{2} \cdot degF)$
Unit of thermal conductivity according to the Imperial system of units
British Thermal Unit (thermochemical Definition) Inch per Square Foot Hour Degree Fahrenheit