Measurement methods


What measurement method?

For conductivity, there are steady-state methods (up to 1200 K) and pulse methods (in particular over 1500 K). If the material under test is a conductor the specimen can be self-heated by passage of an electric current. 

Measuring diffusivity requires an accurate recording of the time dependence of temperature following a transient or periodic temperature perturbation at a specimen boundary. For diffusivity measurement, transient methods are usually preferred. 

As a consequence of the wide ranges of thermal property there is no single method of measurement that can be used for measurement of either property, in particular thermal conductivity. To obtain acceptable values for the measured property, the material type and its range of property value over its operational temperature range will influence particularly the type of method used and the size and conjunction of the test specimen and apparatus. 

In general, thermal conductivity is measured by steady-state techniques and thermal diffusivity by transient techniques. It is possible to use some of the latter in a modified way to also measure thermal conductivity. A measurement method has to be selected depending on the following criteria: 

  • possible sample size and shape
  • temperature range, which is limited for individual techniques 
  • thermal conductivity range, because low conductivity materials like insulating materials or foams need different methods than for high conductivity materials such as metals 

The table below provides short descriptions of the most commonly used measurement methods. Click on the Measurement method for further details.

Common thermal conductivity or thermal diffusivity measurement methods

Measurement method

Short description

Material type

T range 
in °C

Property range
in W/(m.K)

Comparative technique


A secondary method of thermal conductivity measurement in which steady-state linear heat flow is established in a stack consisting of a specimen sandwiched between two references and surrounded by a cylindrical guard heater

all solids

0 to 1000

0.2 to 200

Four-probe technique


Thermal conductivity is determined from measurement of the electric resistivity; current and voltage are normally measured with four probes

metals and metallic alloys

20 to 1600

10 to 800

Guarded heat flow method


Similar in principle to the heat flow meter method but used to measure much smaller higher conductivity specimens using different calibration materials and cylindrical guard around the test stack

polymers, rocks, ceramics, foods, some metals and alloys

100 to 300

0.2 to 20

Guarded hot-plate


Steady-state linear heat flow established in a large flat sample (usually in two nominally identical pieces) sandwiched between a controlled and guarded central hot plate and cold plates operating at a controlled lower temperature. A well-established absolute technique having high accuracy, especially at ambient temperatures.

solid, opaque, homogeneous, composites, insulation materials

-180 to 1000

0.0001 to 2

Heat-flow meter method


A secondary steady-state method using a similar configuration to the guarded hot plate but normally using one large self-guarding specimen in conjunction with a heat flux transducer and with the apparatus calibrated with one or more reference materials or transfer standards

insulation materials

-100 to 200

0.007 to 1.0

Hot-box apparatus, either guarded or calibrated (thermal resistance)


Not generally used for materials but for measuring the steady-state thermal transmission properties (U-value) or the thermal conductance of building envelope components and systems. A large specimen is placed between a hot and a cold chamber operating at fixed temperatures, humidity and air flow conditions. A guarded metering box is attached to the central section of the specimen in the guarded hot box while in the calibrated version a well insulated much larger box is calibrated with a transfer standard

systems containing insulation, wood, masonry, glass and other materials and products used for the building envelope

-20 to 40

Thermal conductance range of 0.2 to 5  (mēK)/W

Hot strip method


Very similar in principle to the hot wire method but uses a narrow thin metal foil pressed directly between two specimen pieces as the power source

glasses, foods ceramics, etc

-50 to 500

0.1 to 5

Hot wire method


Three forms available, either a single or crossed resistive wire or two parallel wires a small distance apart. A quasi-steady state method where the thermal properties are obtained from the temperature v. time response due to a heat flux generated by the wire embedded in the specimen. The curve is analysed in accordance with a model based on a solution of the time-dependent heat equation under a particular set of boundary conditions. In principle an absolute method

refractory materials, many solid types including earth minerals, glasses, plastics  granules and, powders, plus fluids and gases

-40 to 1600

0.001 to 20

Laser flash method


Thermal diffusivity is determined from an analysis of  the temperature rise v. time response induced by absorption of a pulse of laser energy

metals, polymers, ceramics

-100 to 3000

0.1 to 1500

Angstrom method


A long thin (0.3 - 0.9 mm diameter,100 - 300 mm long) radiating rod, tube or bar of a good conducting material, assumed to behave as a semi-infinite medium, is heated at one end by a sinusoidal heat source with a period of typically 100 to 150 s. Temperature sensors are attached at two or more positions along the rod axis. Thermal diffusivity is determined from the resulting velocity and amplitude decrease using one of a number of solutions to the mathematical model.

Metals, alloys, graphite, ceramics

25 to 1300

above 0.5

Modified Angstrom method


The partially masked blackened surface of a thin rectangular specimen is irradiated by uniform chopped light at fixed frequencies and the ac temperature excursion on the opposite face monitored as the specimen is moved in small increments. The in-plane thermal diffusivity is then determined from the linear amplitude decay and phase shift curves

diamond, metals, semiconductors, ceramics and polymer multi-layered composites

-100 to 500

Covers a range of six orders of magnitude

Modulated beam technique


Thermal diffusivity is determined from the temperature modulation induced by absorption of the modulated light beam from a xenon lamp or other source

metals, polymers, ceramics

300 to 2000

1 to 500

Needle probe


A modification of the hot wire technique whereby the heat source and temperature measurement sensor(s) are together sealed into a long thin tube which is then directly embedded in the specimen or fixed in grooves cut across the matching surfaces of two specimen pieces. Can be used for in-situ measurements. Some versions use reference materials for calibration although in principle the technique is an absolute one

soils, minerals, solid and molten polymers and foods, rubber, particulates, powders

-50 to 500

0.05 to 20

Photothermal methods


Intensity modulated light is directed onto the specimen surface and the run-time behaviour of the resultant thermal waves is detected. The amplitude and phase change are evaluated as a function of the modulation frequency using appropriate models to obtain the thermal diffusivity or thermal conductivity

small specimens of most solid  material types

-50 to 500

0.1 to 200. Methods also very useful in a qualitative NDT mode 

Pipe test method (radial flow)


Similar in principle to the guarded hot plate but using a long cylinder or tubular specimen wrapped around a central heater with end guard  heaters and employing radial heat flow to measure thermal conductivity and thermal transference

insulation such as  calcium silicates, mineral and refractory fibre blankets, cellular plastics, foamed glass, microporous block and powder products

50 to 800

0.02 to 2, depending on material type and temperature

Contact transient methods - Plane source with pulse transient


Multi-property version of contact transient. A heat pulse generated during an appropriate time through a metal foil on one face of the specimen and the temperature response measured by a sensor attached to the other specimen surface

polymers, rocks, ceramics, some alloys, thermal insulations, liquid samples such as water, oils, molten polymers

-40 to 400

0.05 to 50

Contact transient methods - Plane source with step-wise transient


Similar to the pulse transient with a heat flux generated for an appropriate time

soils, minerals, solid and molten polymers and foods, rubber, particulates, powders, some building materials

-40 to 400

0.05 to 50

Subsecond techniques


Thermal conductivity is determined from the power balance obtained during the cooling part of the rapid heating and cooling of a thin wire. The heat dissipated by the specimen is lost by radiation and conduction

electrical conductors only

700 to 3300

50 to 400