SIST EN ISO 22007-1:2024

Plastics - Determination of thermal conductivity and thermal diffusivity - Part 1: General principles (ISO 22007-1:2024)

This document describes the background to methods for the determination of the thermal conductivity and thermal diffusivity of polymeric materials. Different techniques are available for these measurements and some can be better suited than others for a particular type, state and form of material. This document provides a broad overview of these techniques. Standards specific to these techniques, as referenced in this document, are used to carry out the actual test method.

Kunststoffe - Bestimmung der Wärmeleitfähigkeit und der Temperaturleitfähigkeit - Teil 1: Allgemeine Grundlagen (ISO 22007-1:2024)

In diesem Dokument werden die Grundlagen für Verfahren zur Bestimmung der Wärmeleitfähigkeit und Temperaturleitfähigkeit polymerer Werkstoffe beschrieben. Für diese Messungen stehen unterschiedliche Verfahren zur Verfügung, und für einen bestimmten Werkstofftyp, eine bestimmte Werkstoffbeschaffenheit oder -form können einige Verfahren geeigneter als andere sein. Dieses Dokument gibt einen umfassenden Überblick über diese Verfahren. Die für diese Verfahren entwickelten Normen werden entsprechend den Verweisungen in diesem Dokument für die Durchführung des jeweiligen Prüfverfahrens angewendet.
SICHERHEITSHINWEIS — Die Anwender dieses Dokuments sollten, falls zutreffend, mit der üblichen Laborpraxis vertraut sein. Dieses Dokument beansprucht nicht, sämtliche mit seiner Anwendung verbundenen Sicherheitsprobleme, soweit diese gegeben sind, zu behandeln. Es liegt in der Verantwortung des Anwenders, die angemessenen Maßnahmen in Bezug auf den Gesundheits- und Arbeitsschutz einzuleiten und vor der Verwendung jegliche gesetzliche Anforderungen zu ermitteln.

Plastiques - Détermination de la conductivité thermique et de la diffusivité thermique - Partie 1: Principes généraux (ISO 22007-1:2024)

Le présent document décrit les principes de base des méthodes permettant de déterminer la conductivité thermique et la diffusivité thermique des matériaux polymères. Différentes techniques de mesurage sont disponibles et certaines peuvent être mieux adaptées que d'autres pour un type, un état et une forme particuliers du matériau. Le présent document donne un aperçu général de ces techniques. Les normes propres à ces techniques, telles que mentionnées dans le présent document, sont utilisées pour la mise en œuvre de la méthode d'essai réelle.

Polimerni materiali - Ugotavljanje toplotne prevodnosti in toplotne razpršenosti - 1. del: Splošna načela (ISO 22007-1:2024)

Ta dokument opisuje ozadje metod za ugotavljanje toplotne prevodnosti
in toplotne razpršenosti polimernih materialov. Za te meritve so na voljo različne tehnike, pri čemer so nekatere lahko primernejše od drugih za posamezno vrsto, stanje in obliko materiala. Ta dokument vsebuje obsežen pregled teh tehnik. Za izvajanje dejanske preskusne metode se uporabljajo standardi za te tehnike, kakor je opisano v tem dokumentu.

General Information

• Status: Published
• Public Enquiry End Date: 21-Jun-2023
• Publication Date: 11-Apr-2024
• ICS: 83.080.01 - Plastics in general
• Technical Committee: IPMA - Polimer materials and products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 25-Mar-2024
• Due Date: 30-May-2024
• Completion Date: 12-Apr-2024
• Ref Project: EN ISO 22007-1:2024 - Plastics - Determination of thermal conductivity and thermal diffusivity - Part 1: General principles (ISO 22007-1:2024)

Relations

• Revised: SIST EN ISO 22007-1:2018 - Plastics - Determination of thermal conductivity and thermal diffusivity - Part 1: General principles (ISO 22007-1:2017)
• Effective Date: 19-Jan-2023

Overview

EN ISO 22007-1:2024 - "Plastics - Determination of thermal conductivity and thermal diffusivity - Part 1: General principles" (ISO 22007-1:2024) provides a comprehensive overview of methods used to measure the thermal conductivity and thermal diffusivity of polymeric materials. Published by CEN/ISO in 2024, this third edition updates guidance on transient and steady‑state techniques, clarifies terminology (including the addition of contact resistance), and replaces the term “laser flash” with light flash. The document explains the principles behind measurement approaches and points to the technique‑specific standards that define the actual test procedures.

Key Topics

• Purpose: background and guidance for measuring thermal transport properties of plastics and other polymeric materials.
• Fundamental properties and terms: thermal conductivity, thermal diffusivity, volumetric heat capacity, thermal effusivity, heat pulse, heat flux, and contact resistance.
• Measurement principles:
  • Transient methods (contact and non‑contact): hot‑wire, line‑source, transient plane source, temperature wave analysis, and light flash (formerly laser flash).
  • Steady‑state methods: guarded hot‑plate, guarded heat flow meter and heat flow meter methods.
  • Comparative techniques for low thermal conductivities using temperature‑modulation.
• Test planning and interpretation: selection of appropriate technique depending on material type, form and thickness; influence of convection, radiation and contact resistance; modeling of transient responses for property extraction.
• Reporting and uncertainty: recommended contents for test reports and discussion of sources of measurement uncertainty.

Applications

EN ISO 22007-1 is relevant wherever accurate thermal property data for plastics are required:

• Materials R&D: selecting and characterizing polymer formulations and composites for thermal performance.
• Product design and thermal management: electronics housings, insulation, heat‑dissipating components and packaging.
• Quality control and certification: establishing batch consistency and compliance with thermal performance requirements.
• Simulation and thermal modelling: providing validated inputs (λ, α, specific heat) for finite element and thermal network analyses.
• Independent testing laboratories and accreditation bodies performing plastics testing.

Users typically include polymer scientists, test laboratories, OEM engineers, thermal analysts, regulatory and standards professionals.

Related standards

• ISO 472 (Plastics - Vocabulary) - referenced for terms and definitions.
• Technique‑specific standards cited within EN ISO 22007-1 (e.g., standards for hot‑wire, light flash, guarded hot‑plate methods) - consult the ISO 22007 series and national standards bodies for the exact test method documents.

Keywords: ISO 22007-1, EN ISO 22007-1:2024, thermal conductivity, thermal diffusivity, plastics testing, light flash method, guarded hot‑plate, polymer thermal properties.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2024
Polimerni materiali - Ugotavljanje toplotne prevodnosti in toplotne razpršenosti - 1.
del: Splošna načela (ISO 22007-1:2024)
Plastics - Determination of thermal conductivity and thermal diffusivity - Part 1: General
principles (ISO 22007-1:2024)
Kunststoffe - Bestimmung der Wärmeleitfähigkeit und der Temperaturleitfähigkeit - Teil
1: Allgemeine Grundlagen (ISO 22007-1:2024)
Plastiques - Détermination de la conductivité thermique et de la diffusivité thermique -
Partie 1: Principes généraux (ISO 22007-1:2024)
Ta slovenski standard je istoveten z: EN ISO 22007-1:2024
ICS:
83.080.01 Polimerni materiali na Plastics in general
splošno
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 22007-1
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2024
EUROPÄISCHE NORM
ICS 83.080.01 Supersedes EN ISO 22007-1:2017
English Version
Plastics - Determination of thermal conductivity and
thermal diffusivity - Part 1: General principles (ISO 22007-
1:2024)
Plastiques - Détermination de la conductivité Kunststoffe - Bestimmung der Wärmeleitfähigkeit und
thermique et de la diffusivité thermique - Partie 1: der Temperaturleitfähigkeit - Teil 1: Allgemeine
Principes généraux (ISO 22007-1:2024) Grundlagen (ISO 22007-1:2024)
This European Standard was approved by CEN on 6 March 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 22007-1:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 22007-1:2024) has been prepared by Technical Committee ISO/TC 61 "Plastics"
in collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by SIS.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2024, and conflicting national standards
shall be withdrawn at the latest by September 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 22007-1:2017.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 22007-1:2024 has been approved by CEN as EN ISO 22007-1:2024 without any
modification.
International
Standard
ISO 22007-1
Third edition
Plastics — Determination of
2024-03
thermal conductivity and thermal
diffusivity —
Part 1:
General principles
Plastiques — Détermination de la conductivité thermique et de la
diffusivité thermique —
Partie 1: Principes généraux
Reference number
ISO 22007-1:2024(en) © ISO 2024

ISO 22007-1:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 22007-1:2024(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 2
5 Test methods . 3
5.1 General .3
5.2 Hot-wire method .5
5.3 Line-source method .6
5.4 Transient plane source method .6
5.5 Temperature wave analysis method .7
5.6 Light flash method .8
5.7 Steady-state methods .9
5.7.1 Guarded hot-plate method .9
5.7.2 Guarded heat flow meter method and heat flow meter method .10
5.8 Comparative method for low thermal conductivities using a temperature-modulation
technique .11
5.9 Intercomparison of thermal conductivity and thermal diffusivity methods for plastics .11
6 Test report .11
Annex A (informative) Sources of uncertainty on measuring thermal transport properties .13
Bibliography .18

iii
ISO 22007-1:2024(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 249, Plastics, in accordance with the Agreement on technical cooperation between ISO
and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 22007-1:2017), which has been technically
revised.
The main changes are as follows:
— the terms and definitions which are not used in the document have been deleted from Clause 3;
— a new term contact resistance (see 3.7) has been added;
— laser flash method has been changed to light flash method.
A list of all parts in the ISO 22007 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 22007-1:2024(en)
Plastics — Determination of thermal conductivity and
thermal diffusivity —
Part 1:
General principles
SAFETY STATEMENT — Persons using this document should be familiar with normal laboratory
practice, if applicable. This document does not purport to address all of the safety concerns, if any,
associated with its use. It is the responsibility of the user to establish appropriate safety and health
practices and to determine any regulatory requirements prior to use.
1 Scope
This document describes the background to methods for the determination of the thermal conductivity
and thermal diffusivity of polymeric materials. Different techniques are available for these measurements
and some can be better suited than others for a particular type, state and form of material. This document
provides a broad overview of these techniques. Standards specific to these techniques, as referenced in this
document, are used to carry out the actual test method.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 472, Plastics — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 472 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
heat pulse
heat change in the form of a pulse produced by a heat source (3.2)
3.2
heat source
heater in the form of a wire, strip, plate or foil embedded within or attached to a test specimen or an area
irradiated by incident light, e.g. a laser
3.3
heat flux
q
heat source (3.2) output produced by a planar source per unit time and unit area
Note 1 to entry: It is expressed in watts per square metre (W/m ).

ISO 22007-1:2024(en)
3.4
thermal transient
temporary perturbation of temperature in a system initially at a uniform temperature due to a heat pulse
for a period during which the system does not attain equilibrium
3.5
volumetric heat capacity
product of the density and the specific heat capacity
Note 1 to entry: It is expressed in joules per cubic metre kelvin [J/(m ⋅ K)].
3.6
thermal effusivity
b
heat transport property given by the square root of the product of thermal conductivity and volumetric heat
capacity (3.5):
bc=⋅λρ⋅
p
where
λ is the thermal conductivity in watt per metre kelvin [W/(m · K)];
ρ is the density in kilogram per cubic metre [kg/m ];
c is the specific heat capacity in joule per kelvin kilogram [J/(K · kg)]
p
2 1/2
Note 1 to entry: It is expressed in joules per square metre kelvin square root second [J/(m · K · s )].
3.7
contact resistance
surface thermal resistance
STR
R
thermal resistance due to the conditions of contact of solids
Note 1 to entry: The amount of heat that passes through a unit heat transfer area is proportional to the temperature
difference between its two sides and inversely proportional to the thermal resistance R.
The thermal resistance R of a material of thickness d and thermal conductivity λ is defined as
d
R=
λ
If heat passes in series through different materials, the overall thermal resistance is found as the sum of the individual
materials.
Note 2 to entry: It is expressed in square meter kelvin per watt [(m · K )/W].
4 Principles
Thermal conductivity refers specifically to the mode of heat transfer via conduction. In thermal conductivity
measurements, other modes of heat transfer, such as convection, radiation and mass transfer, can occur.
Where these modes are significant, the measured property is usually referred to as apparent or effective
thermal conductivity. Thermal conductivity is affected by the conditions under which it is measured, such as
temperature and pressure, as well as compositional variation of the material and orientation of the specimen
since some materials are not isotropic.
In steady-state methods, an appropriately sized specimen of simple geometry in contact with a heat source,
together with one or more temperature sensors, which may be combined with the heat source or separate

ISO 22007-1:2024(en)
from it, is allowed to equilibrate at a given temperature. Transient methods may be contact or non-contact. A
thermal transient is produced by a heat pulse to generate a dynamic temperature field within the specimen.
The temperature change with time (temperature response) is measured by one or more sensors which may
be combined with the heat source, placed at a fixed distance from the source or, as in the case of the light
flash method, located on the other side of the specimen. For measuring very thin films (with thicknesses
in the nm range), the thermal reflectance method – an ultra-fast variant of the laser flash analysis – is
[26]
well suited. Two modes are available: rear heating/front detection and front heating/front detection .
In any case, the response is analysed in accordance with a model, and a set of solutions developed for
the representative set-up and designed for the specific geometry and the assumed boundary conditions.
Depending upon the geometry of the specimen and source and the means of generating the temperature
field, one or more thermo-physical properties can be obtained, either separately or simultaneously. Table 1
contains a summary of the characteristics of different types of transient methods and the properties that
may be determined by their use.
NOTE 1 Most unfilled plastics fall into the category of materials of intermediate thermal conductivity (0,1 W/m · K
to 1 W/m · K).
1)
NOTE 2 Poly (methyl methacrylate) and glass fibre board IRMM-440 and glass ceramic BCR-724 have a thermal
conductivity which is in the same range as those of most polymer and polymer-filled materials. Polydimethylsiloxane
and glycerol are well characterized fluid reference materials with thermal conductivities in the same range as those of
plastics.
NOTE 3 The thermal conductivity λ can be obtained by multiplying the thermal diffusivity α with the volumetric
heat capacity such as the specific heat capacity at constant pressure c multiplied by density ρ, i.e. λ = α ∙ c ∙ ρ.
p p
Table 1 — Basic characteristics of transient methods
Heat source/
Mode of heat Heat source/temperature Measured and/or de-
Type of method heat source
generation sensor configuration rived parameters
geometry
λ, α
Hot wire/line source Contact/Line,
a b
Step-wise Combined or separate (c and b in some versions
p
/hot strip strip
of the method)
Pulse transient Plane Pulse Separate α, c , λ
p
Pulse, step-
Transient plane source Contact/Plane Combined α, c , λ
p
wise
Laser, Xenon
Laser or light flash Pulse Separate α, c , λ
p
lamp/Plane
λ = thermal conductivity; α = thermal diffusivity; b = thermal effusivity; c = specific heat capacity.
p
a
One sensor.
b
Two sensors.
Annex A provides information on sources of uncertainty on measuring thermal transport properties.
5 Test methods
5.1 General
A number of test methods have been developed to provide a means of measuring thermal conductivity and
thermal diffusivity based upon the basic principle outlined above. An overview of these methods is given in
the following subclauses. Some of the contact methods are summarized in Table 2. Complete details of the
contact and non-contact test methods described in 5.4 to 5.6 can be found in ISO 22007-2, ISO 22007-3 and
ISO 22007-4.
1) Glass fibre board IRMM-440 and glass ceramic BCR-724 are products supplied by the Joint Research Centre (JRC) of
the European Commission. This information is given for the convenience of users of this document and does not constitute
an endorsement by ISO of the products named.

ISO 22007-1:2024(en)
In contact methods, the accuracy of the measurement result depends strongly on a good thermal contact
between the sensor and the sample. Enough uniaxial pressure should therefore be applied to press the
various parts of the specimen and the heat source together.
NOTE In some cases, heat sink pastes are used to improve thermal contact.
Table 2 — Schematic diagrams of various transient experimental methods showing critical
dimensions
Method Specimen set-up Characteristic Ideal model
parameters
l = specimen length
200d < w
w = specimen width,
p
a
Hot wire
thickness
l > 4w
d = wire probe diameter
p
w = active zone
s
w > 1,5l
s p
l = probe length
p
a
Line source l > 33d
p p
d = probe diameter
p
d > 6d
s p
d = specimen diameter
s
wh,,dt>3 α
s max
w = width, thickness
where
b
Hot plate h = height
t is the maximum
max
d = specimen diameter
s
measurement time
dd−>4 αt
sp max
d = heat source diameter
p
Transient plane
where
d = specimen diameter
b s
source
t is the maximum
max
w = specimen thickness
measurement time
a
Unless the specimen is a liquid, a suitable groove or hole shall be made for the hot wire or line source.
b
Good thermal contact has to be established between the strip or disc and the specimen.
c
Round or rectangular sample geometries are possible.

ISO 22007-1:2024(en)
TTabablele 2 2 ((ccoonnttiinnueuedd))
Method Specimen set-up Characteristic Ideal model
parameters
h = specimen thickness
d /h = ratio between spec-
s
d /h > 5
s
imen diameter (d ) and
s
Laser or light
The diameter d or side
s
thickness (h)
c
flash
length of the sample
1 = IR detector
shall be > 10 mm
2 = power source (laser or
xenon lamp)
a
Unless the specimen is a liquid, a suitable groove or hole shall be made for the hot wire or line source.
b
Good thermal contact has to be established between the strip or disc and the specimen.
c
Round or rectangular sample geometries are possible.
5.2 Hot-wire method
This method can be used to determine the thermal conductivity of polymers as a function of temperature.
A wire heater is placed in a test specimen or between two test specimens of the same material. The
temperature rise is measured either by the wire itself acting as a platinum resistance temperature detector
or by a thermocouple placed in close proximity to the wire. The heater current is switched on and the
temperature rise is measured by the thermocouple as a function of time.
Starting with the Fourier differential formula, it is possible to describe the transient heat flow for an
infinitely long wire as shown in Formula (1):
 
φ r
ΔTr(),t =− Ei − (1)
 
 
44πLλαt
 
where
t is the time, in s;
ϕ is the rate of heat flow generated by the wire, in W;
r is the distance between the heater and the thermocouple, in m;
L is the length of the wire, in m;
λ is the thermal conductivity, in W/(m⋅K);
α is the thermal diffusivity, in m /s (α = λ/ρC );
p
Ei(x) is the exponential integral, given by:
∞
−u
e
−Ei()x = du (2)
∫
u
x
For values of r /4αt less than 1, Formula (2) can be simplified to Formula (3):
φ 4αt
ΔTr(),t =− ln (3)
4πLλ
rC
where
γ
C = e
where γ is Euler’s constant (= 0,577 216).

ISO 22007-1:2024(en)
According to Formula (3), the variation in the temperature, ΔT(r,t), is a linear function of the natural
logarithm of time, and the thermal conductivity of the sample can be determined using Formula (4):
φ
λ= (4)
4πLK
where K is the slope of the linear part of the curve of temperature variation plotted against the natural
logarithm of time.
With the correct specimen and heater dimensions as indicated in Table 2, Formula (4) can be used for
practical applications.
[3] [4] [19]
Details of the test method can be found in ISO 8894-1 and ISO 8894-2 and ASTM C1113 .
5.3 Line-source method
[17]
This technique , sometimes called a needle-probe method, is a variant of the hot-wire method. It uses a
line-source probe in the form of a needle, which permits repeated measurements of thermal conductivity to
be made without destruction of the sensor. This transient method is capable of very fast measurements and is
suited to both melt and solid-state thermal-conductivity measurements. It is not suited to the measurement
of directional solid-state properties in anisotropic materials.
A line source is located at the centre of the specimen being tested. Both the line source and specimen are kept
at a constant initial temperature. During the course of the measurement, a known amount of heat is produced
by the line source, resulting in a heat wave propagating radially into the specimen. The governing formulae
are the same as those for the hot-wire method. The line source takes the form of a needle-sensor probe of
finite length and diameter. Typical probes are 50 mm to 100 mm long and about 1,5 mm to 2 mm in diameter
and contain a heater element that runs the whole length of the needle. A thermocouple sensor located within
the needle, with its sensing point half-way down the length of the probe, measures the temperature rise
associated with the transient. Deviations from the model, such as the finite probe dimensions, require the
probe to be calibrated against a reference material. A probe constant, C, is introduced into Formula (4); it is
the ratio of the actual thermal conductivity of the reference material to that measured by the instrument as
shown in Formula (5):
Cφ
λ= (5)
4πLK
[18]
NOTE 1 Silicone fluids and glycerol have been used as reference materials . If using glycerol as a reference
material, caution is advised since it is sensitive to moisture.
Typical transients show an initial non-linearity due to the heat wave propagating through the finite thermal
capacity of the probe. This is a region of high conductivity and, hence, low slope. With typical melt state
transients, where the specimen has no contact resistance, the transient approaches linearity directly after
it overcomes this effect, typically within a few seconds. The slope of interest is the linear region that follows
the initial non-linearity. Acquisition durations typically range from 30 s to 60 s. This is very important in
gathering melt state thermal-conductivity data because it dramatically reduces the possibility of thermal
degradation.
NOTE 2 Scanning methods have been devised which permit the automated acquisition of data at different
temperatures, so that measurements over a wide range of temperatures are possible. With such methods, the same
specimen that was used for the melt state measurements can be used for solid-state measurements, thereby permitting
measurements across the melt-to-solid transition.
[13]
Details of the test method can be found in ASTM D5930 .
5.4 Transient plane source method
The transient plane source method is capable of measurements of the true bulk properties of materials with
a wide range of thermal conductivities.

ISO 22007-1:2024(en)
[19]
The technique uses a thin, plane, electrically insulated resistive element as both the heat source and the
temperature sensor to measure the thermal conductivity and the thermal diffusivity from one transient
recording. This resistive-element sensor is brought into thermal contact with two halves of a specimen of
the material under investigation. Each of the specimen halves shall have one flat surface so that the sensor
can be fitted snugly between these surfaces.
By supplying constant electrical power to the sensor, which is of known radius, and by recording the increase
in resistance as a function of time, it is possible to deduce both the thermal conductivity and the thermal
diffusivity from one single transient recording. In order to be able to deduce both these heat transport
properties from a single transient recording, it is important that the probing depth, Δp , as shown in
prob
Formula (6), used for the test be larger than the radius but less than the diameter of the sensor.
½
Δp = 2(αt) (6)
prob
where
α is the thermal diffusivity of the sample material;
t is the total time of the transient.
The sensor can have different designs and be composed of different materials. A spiral pattern is in common
use. Nickel and molybdenum have been used as sensing materials, with the sensing spiral and its connecting
leads etched or cut out of a thin foil with a thickness of around 10 µm. Other sensing materials can be used,
provided the sensing material has a reasonably large temperature coefficient of resistivity. The reason
for this requirement is that the sensor is used not only for increasing its own temperature and that of the
specimen near it, but also for recording the temperature changes.
To electrically insulate the sensing material, it is possible to use a variety of materials: so far thin sheets of
®2)
a polymer (Kapton ), a micaceous material and solid sapphire have been used. When selecting insulating
sheets, it is important that these be kept as thin as possible, preferably in the range 25 µm to 100 µm, in order
to guarantee good thermal contact between the sensing material and the flat surfaces of the surrounding
specimen halves.
For analysing the transient recordings, the heat transfer formulae have been solved for a number of
concentric, circular line sources embedded in an infinite medium. To fulfil this condition in a test, the size of
the specimen shall be such that the distance from any part of the sensor to the nearest outer surface of the
specimen is not less than the probing depth. Sensors with diameters from 1 mm to 60 mm have so far been
used successfully.
Details of the test method can be found in ISO 22007-2.
5.5 Temperature wave analysis method
[23],[24]
The temperature wave analysis method describes a procedure for determining the thermal diffusivity
in the thickness direction of a thin polymer film as a function of temperature. It can be used for both solid
and molten polymers at a constant temperature or for a temperature scan. Measurements can be performed
in ambient air or at reduced pressures.
The principle of the method is to measure the phase shift of a temperature wave propagating in the through-
thickness direction of a thin, flat specimen of thickness d, located between backing plates. For this purpose,
electrical resistors are sputtered directly onto, or contacted with, each surface of the specimen, one as the
heater for generating an oscillating heat wave and the other as the thermometer for measuring the oscillating
temperature. If a one-dimensional heat flux is assumed and the specimen can be considered to
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