ISO 23993:2008

Overview - ISO 23993:2008 (Thermal insulation design thermal conductivity)

ISO 23993:2008 provides methods to derive design thermal conductivity values from declared thermal conductivities for thermal insulation used in building equipment and industrial installations. The standard covers operating conditions from −200 °C to +800 °C and defines a system of conversion factors to account for real-world influences on insulation performance. Where applicable, an additional term is included to represent regular insulation-related thermal bridges (for example, spacers).

Key topics and technical requirements

• Declared vs. design thermal conductivity
  • Declared thermal conductivity is the laboratory value determined under reference conditions (see ISO 13787).
  • Design thermal conductivity is the value used in performance calculations adjusted to service conditions.
• Conversion-factor approach
  • Design values are obtained by applying multiplicative conversion factors to declared values and adding a term for regular thermal bridges (Δλ).
  • Conversion factors cover identified influences; they can be taken from Annex A or derived from measured data (e.g., EN 12667, ISO 8497).
• Principal influences accounted for
  • Temperature non-linearity / temperature difference
  • Moisture content
  • Ageing
  • Compression (mechanical load)
  • Convection within the material
  • Thickness effects
  • Regular joints and insulation-related thermal bridges (spacers)
• Annexes and guidance
  • Annex A: normative conversion factors
  • Annex B: worked examples
  • Annex C: approximate values and guidance for practical use
• Normative references
  • ISO 13787, ISO 7345, ISO 8497, ISO 9229, ISO 9053 and related documents for definitions and test procedures.

Applications and who uses ISO 23993

• Thermal engineers and energy modelers use the standard to convert laboratory thermal conductivity data into accurate design inputs for heat-loss, process insulation, and energy-efficiency calculations.
• Insulation manufacturers and product certifiers apply it to declare performance and derive conservative design values for datasheets.
• Plant designers, HVAC and piping engineers employ design λ values to size insulation systems for building services and industrial installations.
• Testing laboratories and consultants use the conversion methodology when test conditions differ from in-service conditions.

Related standards

• ISO 13787 - Determination of declared thermal conductivity
• ISO 7345 - Thermal insulation: physical quantities and definitions
• ISO 8497 - Thermal transmission properties for circular pipes
• ISO 9229 - Thermal insulation vocabulary
• ISO 9053 - Airflow resistance test methods

ISO 23993:2008 enables consistent, traceable, and conservative conversion of lab thermal conductivity data into practical design values for a wide range of temperatures and service conditions, supporting reliable thermal-performance and energy-efficiency assessments.