Reference materials


A reference material is a material for which one or more of its property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus; assessment of a measurement method; or for assigning property values to other materials. (The International Vocabulary of Basic and General Terms in Metrology, or VIM, 1993).
Reference materials are carefully measured and usually certified
materials (see Definitions at NIST for

Some NPL reference materials (metals, ceramic, polymer) used for calibration of thermal property measurement apparatus.

the different kinds of reference material). In the thermal field they are an essential tool for verification and use of instruments that measure thermal properties such as thermal conductivity, diffusivity, expansivity, emissivity, enthalpy and melting point, among others.

Black painted (Nextel® 101-C10 coating) samples calibrated for spectral emissivity and used to verify reflectometric apparatus (CNR-IMGC)

   Reference materials may be used to calibrate measurement instruments, to compare, develop and validate methods and to establish traceability of measurements, i.e. to ensure comparable measurement results between different laboratories. Present standards for the accreditation of testing and calibration laboratories (such as the international standard ISO 17025) stipulate the use of reference materials. Reference materials must be homogeneous and stable, and the certified values must be accurate.
Finding a material that can be used as a reference for more than one property is one of the goals of current research.

As an example, a European research project was set up to investigate the characteristics of Pyroceram® 9606, a material developed by Corning Glass that is a hybrid of ceramic and glassy phases but is distinct in its composition, structure, and behaviour from either a pure ceramic or a pure glass. Its suitability to be used as reference material for thermal conductivity, thermal diffusivity and specific heat capacity has been assessed and soon it will be available as a Certified Reference Material from the IRMM in Belgium, one of the seven institutes of the Joint Research Centre of the European Commission and one of the world's largest reference material producers.

Reference materials are supplied by international organisations (click here for the IRMM catalogue), research institutes (e.g. NIST, NPL, PTB, NMIJ) or by manufacturers and suppliers of instrumentation (e.g. Labsphere, Perkin Elmer). In the table below is a selection of reference materials for emissivity and other IR-optical properties. A fuller list of reference materials for this and other properties, and their suppliers, is available through a search of Reference materials.   

White reflectance standard barium sulphate powder used to prepare reference samples for integrating sphere reflectometers

Reference materials for emissivity & other IR-optical applications

Reference material Property Notes Link
Barium sulphate (BaSO4) Reflectance (has a high diffuse reflectance value in the near IR region) CRM for use in instruments for reflectivity measurement, e.g. integrating spheres & other reflectometers. (Ref: Applied Optics, vol. 16, no.11, pp. 2775-2776)


Spectralon Reflectance (has a high diffuse reflectance value; data up to 2.5 µm) For use in FTIR-spectrometers


Gold Reflectance, emissivity A diffuse gold surface, highly reflecting, low emissivity


Various Transmittance To verify the spectral transmittance of spectrophotometers up to 25 µm


Nextel® 101-C10 coating Emissivity Black paint widely used as a low reflectance coating; important in radiation thermometry and radiometry applications


Nickel, Fecralloy steel, glass ceramic Emissivity Emissivity RMs for use at IR wavelengths up to 13.6 µm and at elevated temperatures


Mirrors & coated metal plates Reflectance Reflectance RMs for use in the wavelength range 2.5 to
55.6 µm and at ambient temperatures


HE6 and HE23, black paint Emissivity Low reflectance coating for high temperature radiation thermometry application up to 1300 °C