The thermal insulation performance index of the thermal insulation material is determined by the thermal conductivity of the material. The smaller the thermal conductivity, the better the thermal insulation performance. In general, materials with thermal conductivity less than 0.23W/(m·K) are called heat insulation materials, and materials with thermal conductivity less than 0.14W/(m·K) are called thermal insulation materials; usually the thermal conductivity is not greater than 0.05W/(m ·K) materials are called high-efficiency insulation materials. Materials used for building insulation generally require low density, low thermal conductivity, low water absorption, good dimensional stability, reliable insulation performance, convenient construction, environmental friendliness, and reasonable cost.

Factors affecting thermal conductivity of thermal insulation materials.

1. The nature of the material. The thermal conductivity of metals is the largest, followed by non-metals. The liquid is smaller and the gas is smallest.

2. Apparent density and pore characteristics. Materials with low apparent density have low thermal conductivity. When the porosity is the same, the larger the pore size, the greater the thermal conductivity.

3. Humidity. After the material absorbs moisture, the thermal conductivity will increase. The thermal conductivity of water is 0.5W/(m·K), which is 20 times larger than the thermal conductivity of air, which is 0.029W/(m·K). The thermal conductivity of ice is 2.33W/(m·K), which results in a greater thermal conductivity of the material.

4. Temperature. The temperature increases, thermal conductivity of the material increases, but the temperature is not significant when the temperature is between 0-50 ℃. Only for materials at high and negative temperatures, the effect of temperature should be considered.

5. Heat flow direction. When the heat flow is parallel to the fiber direction, the thermal insulation performance is weakened; when the heat flow is perpendicular to the fiber direction, the thermal insulation performance of the thermal insulation material is the best.