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
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.
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