ISO 11561:1999

Overview

ISO 11561:1999 - "Ageing of thermal insulation materials - Determination of the long‑term change in thermal resistance of closed‑cell plastics (accelerated laboratory test methods)" defines laboratory procedures to quantify how the thermal resistance of closed‑cell (≈90% closed) plastic insulation changes with time due to gas diffusion. The standard provides accelerated, slice‑based test techniques and scaling rules to predict long‑term thermal performance (including conservative design life‑time values of 25 years or more) without waiting decades for natural ageing.

Key topics and requirements

• Scope: Applies to closed‑cell cellular plastics containing blowing agents and gases whose diffusion alters foam properties over time.
• Two test methods:
  • Method A (slicing & scaling): Periodic thermal resistance measurements on thin specimens (≈10 mm, not less than 6 mm) conditioned at controlled ambient conditions. Results are scaled mathematically to predict thermal resistance for greater thicknesses as a function of time.
  • Method B (simplified design value): A conservative, shorter test to determine a long‑term design thermal resistance (≥25 years) for unfaced, homogeneous materials; suited for product‑level lifetime estimates.
• Conditioning and measurement: Specimens are conditioned at controlled temperature (recommended (23 ± 2) °C) and humidity (typically (50 ± 5) % RH). Thermal resistance testing uses standard heat flow meter or guarded hot‑plate methods (ISO 8301, ISO 8302).
• Ageing mechanics: Recognizes primary stage (thermal drift from fast N2/O2 diffusion) and secondary stage (slow outward diffusion of blowing agents). Includes factors such as damaged surface layers (TDSL), specimen preparation, and inhomogeneities.
• Reporting and precision: Specifies sampling, dimensional measurement tolerances, test intervals and requirements for test reports. Informative annexes provide the analytical model and an example for faced products.

Applications and users

ISO 11561 is practical for:

• Manufacturer R&D and quality control of closed‑cell foam insulation (XPS, PIR, PU foams).
• Independent test laboratories performing accelerated ageing and thermal performance verification.
• Building designers, energy modelers and specifiers who need reliable long‑term thermal resistance values for life‑cycle energy calculations and code compliance.
• Certification bodies and product assessors establishing design life‑time thermal performance.

Benefits include faster, reproducible prediction of long‑term insulation performance, improved energy‑use estimates, and defensible lifetime design values.

Related standards

• ISO 7345 (thermal insulation - quantities & definitions)
• ISO 8301 (heat flow meter apparatus)
• ISO 8302 (guarded hot plate apparatus)
• ISO 9346 (mass transfer - definitions)

Keywords: ISO 11561, ageing, thermal insulation, closed‑cell plastics, thermal resistance, accelerated laboratory test methods, slicing, scaling, Method A, Method B, design life‑time, diffusion, blowing agent.