# Thermal Insulation Terms

## λ (W/mK) Thermal Conductivity Coefficient

Thermal conductivity coefficient lambda (λ) indicates how much heat a material transmits depending on its physical and chemical structure.

Thermal conductivity coefficient W/mK unit is the quantity of heat transmitted vertically between 1 m2 surfaces of a thermal insulation material with a distance of 1 m when the temperature difference is 1OC.

The smaller a material’s thermal conductivity value is, the less heat it transmits. In other words, the material’s thermal insulation performance increases as this value decreases (Figure 1). Thermal conductivity value is used in preparing thermal insulation projects of buildings together with material thickness.

## U (W/m2K) Thermal Transmittance Coefficient

Thermal transmittance coefficient W/m2 K unit is the quantity of heat transmitted vertically from a surface of 1 m in 1 hour when the difference between the temperatures of two parallel surfaces of a material with a thickness of d (m) is 1K=1oC. U value is dependent on thermal conductivity coefficient (λ) of materials, and their thickness in the direction of heat transmission.

The smaller the thermal transmittance coefficient is, the lesser heat loss is caused. U value is the energy loss per square meter. With a basic approach, the multiplication of energy unit price and the building’s surface are and U values show the financial loss arising from energy loss.

## R (m2K/W) Thermal Transmittance Resistance

Thermal transmittance resistance (R value) is the resistance of a building material against heat transmission.Thermal transmittance resistance (R) should also be calculated to evaluate the performance of the application conducted or to be conducted.
Thermal transmittance resistance is arithmetically the opposite of thermal transmittance coefficient. It is a measurement of a building material’s thermal quality with relation to its location in the building.

The purpose of insulation applications is to reduce the U value as much as possible. Increasing the R value will allow the U value to decrease. Either the board should be thickened or thermal conductivity coefficient should be reduced to increase the R value.