Thermal conductivity refers to the amount of heat transferred per square meter over a period of 1 second when the temperature difference across the two surfaces of a 1-meter-thick material is 1 °C (K or °C); it is denoted by λ and has the unit of watts per meter per kelvin [W/(m·K)].
As is well known, the primary modes of heat transfer are conduction, convection, and radiation. To reduce the thermal conductivity of insulation materials, their structural design should maximize the barrier against heat transfer. Since the thermal conductivity of stationary air is very low, the structural design of insulation materials should incorporate very small pores—so small that air cannot flow freely within them—thereby significantly reducing the efficiency of heat transfer by air convection; furthermore, the smaller the diameter of the material's fibers, the lower the efficiency of heat transfer along those fibers; if aluminum foil is applied to the surface of the insulation material, the heat transferred by radiation will be reflected back, further reducing the efficiency of this mode of heat transfer. Insulation materials possessing the aforementioned structural and design characteristics exhibit very low thermal conductivity and possess excellent thermal insulation performance.
Both composite magnesium silicate insulation materials and aerogel thermal insulation materials exhibit very low thermal conductivity, which is attributable to the comprehensive integration of the aforementioned considerations throughout both the structural design and material compounding processes; as a result, they represent high-performance insulation materials.
