The second generation HFM-100 / HFM-50 instrument is an excellent choice when making steady-state thermal conductivity measurements of specimens such an insulation products and construction materials. Thermtest has rigorously engineered the Heat Flow Meter (HFM) to meet the requirements of international standards including ASTM C518, C1784, ISO 8301, JIS A1412, EN 12667, and EN 12664. Operating the HFM is straightforward—a sample is positioned between two heating – cooling plates, and the upper plate, powered by stepper motors positioned in each corner, lowers to contact the top of the sample. Plate contact with the test specimen is controlled by a standard applied pressure, or by a user defined specimen thickness.
Stepper motors are controlled by individual optical encoders for measurement of sample thickness (L), to the nearest 0.05 mm (0.0019 in). Integrated logic between stepper motors allows the upper plate to sense and adjust for specimens with surface variations, optimizing plate – specimen contact for measurements. One heat flux sensor is integrated into each plate, and is used to monitor heat flux (Q/A), generated due to the difference in temperature (ΔT) between the top and bottom plate at regular intervals, until steady-state heat flux is observed. The composite heat flux is then used to measure thermal resistance (R) and calculate thermal conductivity (λ) according to Fourier’s Law.
Insulation, Solids, and Textiles
Type of Sensors
Flux Sensors (x2)
Three for each flux sensor
Thermal Conductivity Range
0.002 to 0.5 W/m•K (0.001 to 3.5 BTU/(hr·ft·°F))
Specific Heat Capacity
High Thermal Conductivity Kit
Up to 2.5 W/m•K (17.3 BTU/(hr·ft·°F)
30 to 40 min.
± 0.5 to 1%
± 1 to 2%
Plate Temperature Range†
20 to 70 °C（-4 to 158 °F)
HFM-100 Sample Size
Up to 300 x 300 x 100 mm（12 x 12 x 4 in)
HFM-50 Sample Size
Up to 200 x 200 x 50 mm (8 x 8 x 2 in)
ASTM C518, C1784, ISO 8301, JIS A1412, EN 12667, and EN 12664
Method is continually improved; specifications are subject to change without prior notice.
*Performance verified with NIST 1450d / 1450e
†Chilled circulator required
Accurate sample thickness is optimal for determining thermal resistance of a material with the measurement of thermal conductivity. The HFM system features the advantage of either an automatic determination of sample thickness, for rigid materials, or a user defined sample thickness, for compressible materials. Sample thickness is measured using digital optical encoder technology. Four encoders are positioned at each corner of the top sample plate. Multi-position encoder placement ensures the most accurate (< 0.05 mm / 0.0019 in) measurement of sample thickness, and in the end, thermal resistance for materials being measured.
The HFM offers users two versatile and convenient methods of operation—run your measurements independently using the integrated front control panel, or by using the feature packed Windows based HFM-100 software included with each system. The simple to use software offers additional features over the front panel operation, including unlimited steps of temperature automation when testing, and additional functions like saving, exporting, and printing measurement results. With front panel control, users can automate up to five steps of temperature when making measurements, or unlimited steps with the HFM software. HFM results are conveniently available in both SI, and Imperial Units of measure.
Every HFM system comes complete with one Standard Reference Material (SRM) from the National Institute of Standards and Technology (NIST). SRM 1450e- Fibrous Glass-Board is certified for thermal conductivity from 6.85 to 66.85 ̊C (44.33 to 152.33 ̊F), and is available in a thickness of 25 mm (1 in). Additionally available is SRM 1453 – Expanded Polystyrene Board is certified for thermal conductivity from 7.85 to 39.85 ̊C (46.13 to 103.73 ̊F), and is available in a thickness of 12.5 mm (0.5 in). In addition to NIST Standard Reference Materials, Thermal Transfer Standards (TS) can be developed by Thermtest, for specialized testing applications.
The sample should have parallel surfaces. Sample height is automatically measured by the HFM; however for compressible materials, desired sample thickness can be manually entered for predetermined testing thickness.
Place the sample between the HFM’s parallel testing plates. For smaller samples or samples of differing shapes from the testing chamber, place the sample within the center of the lower plate, positioned directly over the heat flux sensor.
A single mean temperature or steps of temperature may be selected for an automated testing routine. Testing can be performed in either quality control or high accuracy (30 to 40 min.) modes for test times which best fit your application. Once testing is complete, results can be saved, printed, or exported to Microsoft Excel for further processing.
Approximate Time: 30 – 40 min.
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