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NPL has one of the world's most comprehensive suite of facilities for measuring the thermal conductivity and thermal resistance of engineering and construction materials. Most of these facilities have been developed in-house to achieve the highest levels of accuracy and they represent the UK national standard for thermal conductivity measurement.

Thermal conductivity ('k value') is a property of a material that determines how much heat is conducted through it for a given temperature difference. However, with a fibrous or porous insulation, which will include both solid material and gas, heat transfer is by a combination of conduction, convection and thermal radiation. 'Thermal conductivity' is still normally the quoted property for such insulation products although strictly it is an 'effective thermal conductivity'.

Thermal resistance ('R value') is a property of an object that determines the resistance to heat transfer through it a for a given temperature difference. As the 'thermal resistance' refers to an object, as opposed to a particular material, it can be used to describe the insulating effect of products that are constructed of layers of different materials. The resistance of an object to heat flow will be greater if it is thick and made from low thermal conductivity materials.

Axial heat flow meter
Guarded heat flow meter
High-temperature guarded hot plate
Low-temperature guarded hot plate
Thermal conductivity by thermal diffusivity
Reference materials and transfer standards

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