Insulation Thermal Conductivity and R-value

The thermal conductivity of an insulation material is an important factor to consider when choosing insulation for a building or an industrial application. Insulation materials are used to reduce heat transfer by conduction, convection, and radiation. By reducing heat transfer, insulation helps to keep a building or other structure warm in the winter and cool in the summer, reducing the energy required to maintain a comfortable indoor temperature. The same principle applies to process lines in an industrial site.

The thermal conductivity of an insulation material determines how well it will perform in reducing heat transfer. Materials with low thermal conductivity are better insulators, as they provide more resistance to heat flow. For example, materials like aerogels, rockwool stonewool, fiberglass, and foam insulation have low thermal conductivity, making them effective insulation materials.
Thermal conductivity is measured in [W/(m·K)] metric units or in [Btu·in/(h·ft2·°F)] with imperial units.

The R-value of insulation refers to its thermal resistance, which is a measure of its ability to resist heat flow. The higher the R-value, the better the insulation’s ability to reduce heat loss or gain.

The R-Value of a flat material is determined by dividing the thickness of the material (in meters) by the thermal conductivity (in W/m.K). The Total R-Value of the construction is the sum of the thermal resistance of each layer, surface air film resistance, and any bridged layers.

For pipe insulation, the heat flow is not the simple straight-through heat-flow found for flat sheet material, but rather radial heat flow. This is true because the inner radius surface is much smaller than the outer radius surface area. Because of these differences in surface area, the R-value of pipe insulation is calculated using the following equation: Rtube= r2* ln(r2/r1) / K with r1 being the inner radius of the pipe insulation (m), r2 the outer radius of the pipe insulation and K the thermal conductivity of the material in [W/(m·K)].

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