Thermal resistance

Thermal resistance measures how strongly an object or layer impedes heat flow. It is the temperature difference across the object divided by the heat-transfer rate through it.

Fourier's law: A law stating that conductive heat flux is proportional to the negative temperature gradient. It relates temperature gradients and material conductivity to resistance against conduction.
Thermal insulation: Materials or systems that reduce heat transfer between regions at different temperatures. Insulation works by adding substantial resistance to heat flow.
Heat transfer: The movement of thermal energy from hotter regions to colder regions. Thermal resistance quantifies opposition to this energy transfer.
Thermal conductance: The heat-transfer rate through a body per unit temperature difference across it. Conductance is the reciprocal of total thermal resistance.
Thermal conductivity: A material property that measures its ability to conduct heat. Low conductivity increases a layer’s resistance to heat flow.
R-value: A measure of thermal resistance used to rate building insulation. It expresses resistance per area for comparing insulation products.
Temperature difference: The difference in temperature between two locations or states. It is the driving difference across a thermal resistance.
Thermal resistivity: A material property equal to the reciprocal of thermal conductivity. It describes material opposition per unit length, while resistance also depends on geometry.
Thermal contact resistance: The resistance to heat transfer across the interface between two contacting bodies. An interface can add resistance beyond that of either solid layer.
U-factor: The rate of heat transfer through a building component per unit area and temperature difference. It is the inverse of area-normalized resistance for the same component.

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