The HFM-100 Heat Flow Meter method is an easy-to-use rapid
technique for thermal conductivity and thermal
resistance measurement.

Best For insulation products, construction materials, packaging, and assemblies

ASTM C518 | ISO 8301 | EN 12667

Standard Test

-20°C to 70°C


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A measurement of thermal conductivity is an indicator of the ability of a material to conduct heat and can be critical for defining energy efficiency and thermal performance in materials. The Thermtest HFM has been designed and engineered to combine the highest accuracy, repeatability, widest temperature range, and industry-leading performance, all at an exceptional value. Follows international standards: ASTM C518, ISO 8301, and EN 12667.

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    HFM-100 Features

    The second generation HFM-100 instrument is an excellent choice when making steady-state thermal conductivity measurements of specimens such as insulation products and construction materials. Thermtest has rigorously engineered the Heat Flow Meter (HFM) to meet the requirements of international standards including ASTM C518, ISO 8301, and EN 12667. 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.

    HFM-100 equation

    • Two flux sensors with surface thermocouples for accurate measurement of thermal resistance and thermal conductivity
    • Multiple Peltier heating / cooling plates for rapid control of temperature
    • Thickness is measured to an accuracy of 0.05 mm (0.0019 in) with the use of four digital optical encoders
    • Front panel operation allows full control of all HFM functions, or use the new feature packed HFM-100 Software for basic and additional functions, such as printing and exporting
    • Plate clamping can be automated or set to a user defined thickness—ideal for compressible materials
    • Follows international standards: ASTM C518, ISO 8301, and EN 12667

    Following international standards, the HFM 100 is designed for testing both homogeneous and heterogeneous materials. The HFM 100 sample size allows for representative testing of materials typically found in insulation and construction industries.

    Materials Insulation, Solids, and Textiles
    Type of Sensors Flux Sensors (x2)
    Surface Thermocouples Three for each flux sensor
    Applications General Testing
    Direction Through-Thickness
    Thermal Conductivity Range 0.002 to 0.5 W/mK (0.001 to 3.5 BTU/(hr·ft·°F))
    Specific Heat Capacity Optional
    High Thermal Conductivity Kit Up to 2.5 W/m•K (17.3 BTU/(hr·ft·°F))
    Measurement Time 30 to 40 min
    Reproducibility ± 0.5 to 1%
    Accuracy* ± 1 to 2%
    Plate Temperature Range -20 to 70°C (-4 to 158˚F)
    Maximum Sample Size Up to 300 x 300 x 100 mm (12 x 12 x 4 in)
    Standard ASTM C518, ISO 8301, and EN 12667

    Method is continually improved; specifications are subject to change without prior notice.
    *Performance verified with NIST 1450D / 1450E
    Chilled circulator required

    Heat Flow Meter Method Highlights
    Measurement of Heat Flux
    Measurement of Heat Flux

    A heat flux sensor is a thermopile sensor, consisting of thermocouple junctions arranged uniformly across the sensor surface. Each individual junction generates an electrical voltage, proportional to the difference in temperature across the hot and cold junctions of the thermocouple. For accurate measurements of heat flux, one flux sensor with three surface thermocouples is integrated into the surface of each testing plate of the HFM. This intimate contact reduces the level of calibration required, resulting in improved test results.

    Temperature Control
    Temperature Control

    Thermoelectric Peltier elements are used to heat and cool the HFM testing plates. A thermoelectric element is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. This flexibility allows the user to easily change heating, and cooling direction, to best match their testing application, at a temperature resolution of <0.01°C (0.018°F). Each plate contains multiple high power thermoelectric modules, matched with a surface thermocouple, and smart temperature control to optimize the speed, and accuracy of the plate temperatures.

    Thickness Measurement
    Thickness Measurement

    Accurate sample thickness is optimal for determining thermal resistance of a material with the measurement of thermal conductivity. The HFM-100 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.

    Versatile Operation
    Versatile Operation

    The HFM-100 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.

    Sample Measurements
    The Sample
    The Sample

    The sample should be between 150 mm,and 300 mm square (6 in to 12 in square), and have parallel surfaces. Sample height is automatically measured by the HFM-100; however for compressible materials, desired sample thickness can be manually entered for predetermined testing thickness.

    Approximate Time: 1 minute

    Insert Sample
    Insert Sample

    Place the sample between the HFM-100’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.

    Approximate Time: 1 minute

    Close Plates
    Close Plates

    The top plate automatically lowers for rigid samples or to a predetermined thickness for compressible samples. For added accuracy when testing rigid samples, the top plate makes a short confirming movement for optimum contact, and measurement of thickness. Additionally, this short movement will also compensate for any issue with sample flatness.

    Approximate Time: 1 minute

    Run Experiment
    Run Experiment

    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 60 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 minutes

    Insulation vs. Temperature

    Insulation vs. Temperature

    The Thermtest HFM-100 is capable of testing materials over a temperature range of -20 to 70°C (-4 to 158˚F). NIST 1450d, Fibrous Glass Board, is a certified Standard Reference Material from the National Institute of Standards, and Technology. Measured results are within 2% of the certified values.


    High Thermal Conductivity Kit

    High Thermal Conductivity Kit

    With the added High Thermal Conductivity Kit, the HFM-100 is able to accurately, and efficiently measure higher thermal conductivity materials, such as glass and ceramics. For such applications, an external thermocouple kit is used in combination with the sample being tested. Macor, Quartz, and Pyrex were tested in the HFM from 10˚C to 60˚C (50˚F to 140˚F). All measured values are within the stated accuracy of the system, ± 5%.

    Batting Insulation
    Batting Insulation

    Both a fiberglass and a stone wool batting insulation were tested with the HFM. A thermal conductivity of 0.0430 W/m•K (0.2981 BTU/(hr·ft·°F)) was the result of the fiberglass testing, where 0.0364 W/m•K (0.2524 BTU/(hr·ft·°F)) was the result of the stone wool insulation test.


    Aerogel has one of the lowest thermal conductivities known to solids. An aerogel blanket of choice was selected to test by the Heat Flow Meter. Results concluded a thermal conductivity of 0.024 W/m•K (0.1664 BTU/(hr·ft·°F)), which is within 3% to the manufacturers specification.


    As wood is rigid, the HFM can be set to automatically adjust to the height of the sample. Testing of this softwood produced a thermal conductivity reading of 0.12 W/m•K (0.8320 BTU/(hr·ft·°F)), an exact match to the literature values for softwoods.

    Heat Flow Meter Accessories

    External thermocouple kit


    External thermocouple kit for testing materials up to 2.5 W/mK


    One of our qualified team members will reach out to you to offer a price that fits your needs.

      Featured Webinar

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      In this webinar, Dale Hume dives into testing materials at high temperatures with Thermtest’s new Guarded Heat Flow Meter-01.

      October 6, 2021


      Dale Hume


      Mitchell Robinson

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