We are one of the world-leading National Measurement Institutes in thermal conductivity measurements, and have developed a range of UK national standard facilities for direct thermal conductivity measurements covering temperatures from -170 °C to 800 °C and thermal conductivities from 0.01 W/(m*K) to 240 W/(m*K). We have a range of thermal conductivity reference materials and transfer standards conforming to ISO 17034, to provide traceability for industry worldwide. All our thermal conductivity measurement services using direct methods are UKAS accredited.
Direct measurement of thermal conductivity uses steady state methods and is limited to 500 °C for high conductivity materials and to 800 °C for insulation, but we can derive the thermal conductivity at higher temperatures (to over 1500 °C) using values of thermal diffusivity, specific heat capacity and density. This provides a relatively fast and cost-effective way of obtaining data over a wider temperature range.
Our thermal diffusivity measurements have been validated against European Certified Reference Material and NMIJ Certified Reference Material. In addition, the Laser Flash (LFA) thermal diffusivity measurements at NPL have been compared with measurements in other National Measurement Institutes (NMIs) in an International Bureau of Weights and Measures (BIPM) Consultative Committee on Thermometry (CCT) Supplementary Comparison, CCT-S3.
Thermal expansion is measured by contact dilatometry and our instruments can cover the range 100 °C to 1550 °C, including measurement of some liquids in a specially designed cell. Phase changes, annealing and hysteresis can be assessed.
Density is measured by the Archimedes method at room temperature and a value for open, or surface porosity can also be determined. By using this and thermal expansion data the density can be calculated over a wide temperature range.
Axial heat flow meter

This flow meter is suitable for measuring thermal conductivity of homogeneous materials.
- Measurements on metals, alloys and graphite
- Thermal conductivity range: 10 W/m·K to 240 W/m·K
- Mean specimen temperature range: 50 °C to 500 °C
- Conforms to NPL procedure QPDQM/B/411
- UKAS accredited test service (UKAS 0002)
- A single specimen is required 160 mm x diameter 20 mm
- A drawing with the specification for the required specimen is available upon application, including holes necessary for mounting the specimen and positioning thermocouples
- Measurements are carried out in the normal air environment.
- We can help prepare specimens if you do not have a machining facilities
Guarded heat flow meter
This heat flow meter is a commercial apparatus for measuring thermal conductivity or thermal resistance
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- Thermal resistance range: 0.001 m²·K/W to 0.03 m²·K/W
- Temperature range -80 °C to 250 °C
- Conforms to ASTM E1530-11
- UKAS accredited test service (UKAS 0002)
- A single specimen is required, thickness: 1 mm to 20 mm, diameter: 50.8 mm, variation in thickness should be less than 0.025 mm
- Maximum mean specimen temperature to be at least 20 °C below the softening point of the test specimen.
High-temperature guarded hot plate
This hot-plate is an NPL designed and built national standard for thermal conductivity or thermal resistance of insulation and refractories at high temperatures.
- Thermal conductivity range: up to 0.5 W/m·K
- Thermal resistance range: greater than 0.07 m²·K/W
- Mean specimen temperature range: 140 °C to 800 °C
- Conforms to ISO 8302:1991
- UKAS accredited test service (UKAS 0002)
- A single specimen is required (Thickness: 25 mm to 50 mm, Diameter: 305 mm, flatness: better than 0.2 mm
Low-temperature guarded hot plate.jpg.aspx?width=306&height=268)
This guarded hot-plate is an NPL designed and built national standard for thermal conductivity or thermal resistance of insulation at low temperatures.
- Thermal conductivity range: up to 0.15 W/(m·K)
- Mean specimen temperature range: -170 °C to 50 °C
- Conforms to ISO 8302:1991 and EN 12667:2001
- UKAS accredited test service (UKAS 0002)
- An identical pair of specimens is required. (thickness: 25 mm to 50 mm, length and breadth: 305 mm x 305 mm, flatness: better than 0.2 mm)
Thermal conductivity by thermal diffusivity
The laser flash apparatus (LFA) is an instrument used to measure the thermal diffusivity (a) of materials with respect to temperature. This can then be used to calculate thermal conductivity (λ) if the density (ρ) and specific heat (Cp) of the sample as a function of temperature are already known. It has a temperature range from 25 °C to 1600 °C (or 2000 °C with modifications).
The LFA may be used to assess thermal diffusivity of a wide range of materials including metals and alloys (in solid and liquid phases), ceramics, hard metals, coated materials and MMCs.
- Thermal diffusivity range: 0.01 mm2/s to 1000 mm2/s
- Temperature range: 25 °C to 2000 °C
- Sample dimensions: 6 mm, 10 mm or 12.7 mm diameter
- Inert, static and dynamic atmosphere conditions
We are one of the world-leading National Measurement Institutes in thermal conductivity measurements, and have developed a range of UK national standard facilities for direct thermal conductivity measurements covering temperatures from -170 °C to 800 °C and thermal conductivities from 0.01 W/(m*K) to 240 W/(m*K). We have a range of thermal conductivity reference materials and transfer standards conforming to ISO 17034, to provide traceability for industry worldwide. All our thermal conductivity measurement services using direct methods are UKAS accredited.
Direct measurement of thermal conductivity uses steady state methods and is limited to 500 °C for high conductivity materials and to 800 °C for insulation, but we can derive the thermal conductivity at higher temperatures (to over 1500 °C) using values of thermal diffusivity, specific heat capacity and density. This provides a relatively fast and cost-effective way of obtaining data over a wider temperature range.
Our thermal diffusivity measurements have been validated against European Certified Reference Material and NMIJ Certified Reference Material. In addition, the Laser Flash (LFA) thermal diffusivity measurements at NPL have been compared with measurements in other National Measurement Institutes (NMIs) in an International Bureau of Weights and Measures (BIPM) Consultative Committee on Thermometry (CCT) Supplementary Comparison, CCT-S3.
Thermal expansion is measured by contact dilatometry and our instruments can cover the range 100 °C to 1550 °C, including measurement of some liquids in a specially designed cell. Phase changes, annealing and hysteresis can be assessed.
Density is measured by the Archimedes method at room temperature and a value for open, or surface porosity can also be determined. By using this and thermal expansion data the density can be calculated over a wide temperature range.
Thermal conductivity reference materials and transfer standards
NPL transfer standards are measured in one of our national standard apparatus and is provided with a certificate showing traceability to the UK national standards and UKAS accreditation (UKAS 4002) for producing reference materials to ISO 17034:2016.
Material: EXPANDED POLYSTYRENE
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Lateral dimensions:
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305 mm x 305 mm
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Thickness range:
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25 mm to 50 mm
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Temperature range:
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-150 °C to 50 °C
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Number of temperature:
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5
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Estimated uncertainty:
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±2.0%
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Guarded Hot Plate:
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LTGHP
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NPL reference material specimens are cut from a batch of material that has been characterised by a series of measurements on material that is known to have stable and predictable properties. They have a higher calibration uncertainty than the equivalent transfer standard due to the contribution of variation within the batch. They are provided with a certificate showing traceability to the UK national standards and UKAS accreditation (UKAS 4002) for producing reference materials to ISO 17034:2016.
Material:
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STAINLESS STEEL 304
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INCONEL 600
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PURE IRON
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Diameter:
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60 mm
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60 mm
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25 mm
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Temperature range:
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100 °C to 500 °C
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100 °C to 500 °C
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100 °C to 500 °C
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Estimated uncertainty:
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±4.8%
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±4.8%
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±6.1%
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NPL batch code:
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NPL 2S09
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NPL 2I09
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NPL Fe09
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Material: PERSPEX (polymethylmethacrylate)
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Maximum dimensions: 305 mm x 305 m
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Maximum thickness: 31 mm
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Temperature range: -10 °C to 60 °C
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Estimated uncertainty: ±4.0%
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NPL batch code: NPL 05/01
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