Overview
ISO 2796:1986 specifies a laboratory method to determine the dimensional stability of rigid cellular plastics (rigid foams). The test measures irreversible changes in linear dimensions when specimens are exposed to specified environments of temperature and relative humidity for defined periods and then reconditioned. The method provides a range of test atmospheres so users can select one or more relevant conditions.
Key topics and requirements
- Specimen size and preparation
- Nominal specimen: 100 mm × 100 mm × 25 mm (minimum tolerances apply).
- Surfaces should be smooth (machined or cut) and, unless otherwise specified, surface skin removed.
- At least three specimens per sample per test condition.
- Conditioning and exposure
- Initial conditioning in a normal atmosphere per ISO 291.
- Test exposures use a selectable range of temperatures (from sub-zero to high temperatures) and humidities (including 90–100% RH for high-humidity atmospheres).
- Specimens are placed horizontally on a perforated support with free air circulation and a minimum 25 mm spacing; avoid direct radiant heating.
- Test schedule
- Measurements and reconditioning are performed after 20 ±1 h, 48 ±2 h, and optionally 7 days and 28 days total exposure.
- After each exposure interval, specimens are reconditioned for 1–3 hours before measuring.
- Measurement
- Linear dimensions measured in accordance with ISO 1923: length and width at three positions, thickness at five positions.
- Calculate percentage variation using the mean pre-test and post-test dimensions.
- Measurement instrument accuracy should comply with ISO 1923 requirements.
- Reporting
- Test report must identify the standard, specimen details, conditioning method, test conditions, per-specimen percent changes and means, visible deformations, and any procedural deviations.
Practical applications and users
- Quality control and incoming inspection for manufacturers of rigid cellular plastics (insulation panels, structural foam cores).
- Research and development to compare formulations or processing effects on dimensional stability.
- Independent testing laboratories and certification bodies verifying material performance under environmental stress.
- Procurement engineers and specifiers who need objective stability data for design or acceptance criteria.
Related standards
- ISO 291 - Conditioning atmospheres for plastics.
- ISO 1923 - Methods for measuring linear dimensions of plastics (used for measurement technique and instrument accuracy).
Keywords: ISO 2796:1986, rigid cellular plastics, dimensional stability test, specimen size, conditioning, temperature and humidity, ISO 291, ISO 1923, linear dimensions.
