HFM – Heat Flow Meter

Thermal conductivity meter for testing insulation materials


On point

The LINSEIS Heat Flow Meter is a fast and user-friendly instrument designed for the precise determination of thermal conductivity properties in low thermally conductive insulation materials, as well as other materials. Its unique design enables quick measurements with a high level of accuracy, with results obtained in minutes.

Utilizing Peltier heating and cooling technology, the instrument offers highly precise temperature control while reducing maintenance requirements and downtime. Exceptional long-term stability ensures accurate data for extended aging studies. The instrument can achieve rapid measurement cycles, with intervals as short as 15 minutes, resulting in a high sampling rate.

To facilitate these fast and accurate sampling intervals, the instrument employs a dual sensor arrangement. It also features built-in potentiometers that provide length measurements with a resolution of micrometers, offering immediate data on sample thickness. This comprehensive setup enables efficient and reliable thermal conductivity measurements for a wide range of materials.

This design facilitates outstanding reproducibility and enables exceptional temperature control and heating rates of up to 100 K/min. The integrated sensor is user-replaceable and available at a low cost.

HFM features of the “updated version”:

  • Clean system design with improved isolation and optimized electronics
  • Unmatched precision and accuracy
  • Low power consumption
  • Instrument design based on the standards ASTM C518, JIS A1412, ISO 8301, DIN EN 12664 and DIN 12667

Key benefits

Short Test Cycles

The LINSEIS Heat Flow Meter incorporates a double heat flux sensor configuration to achieve the shortest possible measurement cycles. In most cases, a typical measurement can stabilize in as little as 15 minutes, ensuring rapid results.

Highest Accuracy

The instrument is equipped with two built-in linear potentiometers, enabling automated and highly precise determination of sample thickness. Two heat flux sensors are utilized to precisely measure the heat flow, which is defined between the hot and cold plates.

Zero Maintenance

The system is designed to be rugged and features a unique zero maintenance Peltier heating and cooling cycle, resulting in minimal maintenance costs. This design ensures long-term reliability and consistent performance of the instrument.

Unit operation

The heat transfer coefficient (U-value) can be determined by dividing the measured heat flow through the sample by the cross-sectional area and the applied temperature difference. In the case of a homogeneous material, the thermal conductivity (Lambda) can be calculated by multiplying the U-value with the sample thickness.


This calculation is based on Fourier’s law of heat conduction, which forms the foundation for determining thermal conductivity and thermal resistance in materials. It relates the heat flow rate to the temperature gradient within a material, enabling the quantification of how well a material conducts heat.

Integrated dew protection system

To prevent moisture content from affecting thermal conductivity

When an object’s temperature drops below the ambient temperature and reaches the dew point of the surrounding air, the moisture in the air will start to condense on that object. This phenomenon can also occur when samples are inserted into the Heat Flow Meter (HFM) and are supposed to be measured at temperatures below the dew point. The condensed humidity, or dew, may be absorbed by the sample, potentially altering its thermal conductivity.

To mitigate this issue, one approach is to replace the surrounding air with dry air or nitrogen and maintain a constant gas flow throughout the entire measurement process. The Linseis HFM is equipped with the necessary components, including a throttle valve and a flow meter, which are integrated to facilitate this precise, stable, and reproducible measurement process. This ensures that the thermal conductivity of the sample remains consistent and unaffected by condensation.

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All facts on your hand

Model HFM 200 HFM 300 HFM 600
Temperature Range (Plates): 0 to 90°C
-20 up to 90°C
-40 up to 90°C
0 to 90°C
-20 up to 90°C
-35 up to 90°C
-20 to 70°C

Cooling system: External chiller or thermostat External chiller or thermostat External chiller or thermostat
Temperature control (Plate): Peltier Peltier Peltier
Temeprature resolution: 0.0001 °C 0.0001 °C 0.0001 °C
Measurement Data points: up to 100 up to 100 up to 100
Sample size: 200 mm x 200 mm, up to 90 mm thickness 300 mm x 300 mm, up to 100 mm thickness 600 mm x 600 mm, up to 200 mm thickness
Th. resistance measuring range: 0.2 to 8.0 m2k/W with extension: 0.036 to 9.0 m2K/W 0.2 to 8.0 m2K/W, with extension: 0.036 to 8.0 m2K/W 0.2 to 8.0 m2K/W, with extension: 0.036 to 8.0 m2K/W
Th. conductivity measuring range: 0.001 to 0.5 W/m∙K, with extension: 0.001 to 2.5 W/m∙K 0.001 to 0.5 W/m∙K, with extension: 0.001 to 2.5 W/m∙K 0.001 to 0.5 W/m∙K
Reproducability: 0.25% / 0,5 % 0.25% / 0,5 % 0.25% / 0,5 %
Accuracy: +/- 1 up to 2 % +/- 1 up to 2 % +/- 1 up to 2 %
Variable contact pressure: up to 1.3 kPa, optional up to 25 kPa up to 1.3 kPa, optional up to 25 kPa up to 1.3 kPa, optional up to 25 kPa


The Linseis Heat Flow Meter can be operated through the touch screen front panel. Optional software free of charge is available. This state of the powerful software package enables convenient temperature programming, data storage and instrument control.

Key features:

  • The instrument can be operated from the touch screen front panel
  • Easy input of measurement parameters
  • Measurement data storage and export
  • Report printing, layout can be customized
  • Multilingual software versions
  • Instrument monitoring (plate temperature, thermal conductivity results, and output signal monitoring)
  • Optional user log-in and data monitoring


Application Example: Elastomer Foam

This measurement serves as a clear demonstration of the exceptional reproducibility of the LINSEIS HFM series. Remarkably, a reproducibility of 0.25% was achieved. The graph displays four measurements of an Elastomer Foam within the temperature range of 15 to 40°C. After each measurement, the sample was removed and then placed back into the instrument, reaffirming the instrument’s ability to consistently and precisely measure the thermal conductivity of the Elastomer Foam.


Fifteen measurements were conducted on the IRMM-440 certified reference material, which is a resin-bonded glass fiberboard. At 30°C, the material exhibited a thermal conductivity of 0.03274 ± 0.00015, and at 15°C, it had a thermal conductivity of 0.03102 ± 0.00012. The X-axis of the graph illustrates the temperature gradient. This demonstrates the repeatability and consistency of the thermal conductivity measurements for this reference material across various temperature gradients.


The graph depicts two measurements of the same glass wool specimen at various temperatures. The black line represents the thermal conductivity as provided by the manufacturer’s information. The X-axis illustrates the temperature gradient. This comparison highlights the precision and accuracy of the thermal conductivity measurements, showing how closely they align with the manufacturer’s specifications across different temperature gradients.

Polyester fibres::

Compressible materials can exhibit changes in their properties based on the degree of compression. This characteristic is also reflected in the thermal conductivity of such materials. To demonstrate this, an experiment was conducted using a mat of polyester fibers. A sample measuring 300 mm x 300 mm with an initial thickness of approximately 60 mm was placed into a Linseis HFM 300 and tested at room temperature.

Using the distance control feature, the upper plate was adjusted step by step, reducing the sample’s thickness to 60 mm, 40 mm, and 20 mm. At each sample thickness, a temperature gradient of 20 K was applied until a stable state was achieved. The compression of the sample resulted in a significant reduction in thermal conductivity, showcasing the impact of compression on this material’s thermal properties.

External application

The Application of Building Physics in the Design of Roof Windows (published Energies)

Rigid Polyurethane Foams as External Tank Cryogenic Insulation for Space Launchers (published IOP Conference Series: Materials Science and Engineering)

THERMAL CONDUCTIVITY OF WOODEN FLOORS IN THE CONTEXT OF UNDERFLOOR HEATING SYSTEM APPLICATIONS (published Wood Investigation and Application Department, Wood Technology Institute, Poznan, Poland)


HFM Product Brochure (PDF)

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