Thermal Conductivity Testing

Scope

Thermal conductivity testing covers the measurement of thermal conductivity (k) and thermal diffusivity (α) of solid materials using the heat flow meter and laser flash methods, with the method selected based on the material’s conductivity range and form.

Key aspects of the testing scope include:

• Heat flow meter (ASTM C518) – steady-state method; a flat specimen sandwiched between temperature-controlled plates with heat flux transducers; provides thermal conductivity directly; suited to thermal insulation, foams, polymers, and low-conductivity materials; results also expressed as thermal resistance (R-value) per unit thickness
• Laser flash (ASTM E1461) – transient method on a small disc specimen; a laser pulse heats one face and an IR detector measures the temperature response on the other; gives thermal diffusivity α, from which thermal conductivity k is derived using density (ρ) and specific heat capacity (Cp): k = α · ρ · Cp; suited to metals, ceramics, composites, and moderate-to-high conductivity materials across a range of temperatures
• Temperature range – measurements at ambient or at elevated/reduced temperatures (laser flash can operate over a wide temperature range, enabling thermal conductivity vs. temperature data)
• Related properties – thermal diffusivity (α), specific heat capacity (Cp, measured separately by DSC), thermal resistance (R-value), and thermal effusivity
• Applicable standards – ASTM C518, ASTM E1461, ISO 22007-2 (transient plane source), and related standards

Applications

• Thermal insulation materials – measuring the k-value of insulation boards, foams, batts, aerogels, and blankets for building and industrial insulation specification
• Polymers and composites – characterizing thermal conductivity of engineering plastics, filled polymers, and fiber-reinforced composites used in structural and thermal applications
• Electronics thermal management – measuring thermal interface materials (TIMs), thermal greases, phase-change materials, and substrate/PCB materials for thermal resistance in electronics cooling design
• Metals and alloys – determining thermal conductivity of aluminum, copper, steel, and specialty alloys for heat exchanger and thermal management design
• Ceramics and refractories – characterizing thermal conductivity of ceramic components, refractory bricks, and advanced ceramics for high-temperature applications
• Battery and energy materials – measuring thermal conductivity of battery electrodes, separators, and other energy storage materials for thermal management
• Construction materials – determining R-values and thermal conductivity of concrete, gypsum board, roof decking, and building materials
• R&D and new material development – providing the thermal conductivity data needed to evaluate and optimize new materials in development

Benefits

• Two complementary methods cover all material types – the heat flow meter and laser flash together span from near-zero conductivity insulation to highly conductive metals, covering the full range of materials in one testing capability
• Directly supports thermal design – k-values and diffusivity data are the primary inputs to thermal simulation and design, so the measurements enable quantitative design rather than assumptions
• Temperature-dependent data available – laser flash testing over a range of temperatures provides k(T) data for materials used across a temperature range, which static ambient measurements cannot provide
• Insulation specification and R-value – ASTM C518 results provide the k-value and R-value needed to specify insulation materials to energy code requirements
• Enables comparison and selection – testing candidate materials under the same conditions provides an objective basis for selecting the best thermal conductor or insulator for an application
• Supports quality control – thermal conductivity is sensitive to material composition, density, and processing, making it an effective QC parameter for thermally critical materials