| Feature | ASTM D618-21 | ISO 291 | | :--- | :--- | :--- | | Standard Temp | 23°C ± 2°C | 23°C ± 2°C | | Standard RH | 50% ± 5% | 50% ± 10% (looser) | | Conditioning Time | 40 hours min | 88 hours (for most materials) | | Test Time Limit | Immediate | Within 15 minutes |
A: A calibrated hygrometer with accuracy of ±2% RH or better.
A: No. D618-21 requires closed, controlled chambers with active humidity control. astm d618-21 pdf
A: No. This standard applies only to solid molded, extruded, or cast specimens.
The "21" denotes the year of last approval—2021. While the standard is reaffirmed periodically, the 2021 version currently contains the most up-to-date requirements for humidity control, temperature tolerances, and testing timelines. Plastics are hygroscopic or hydrophobic to varying degrees. Nylon absorbs moisture from the air, becoming more flexible and impact-resistant. Polycarbonate, on the other hand, can become brittle if too dry. Without a standard like ASTM D618, one laboratory might test "dry-as-molded" nylon while another tests nylon conditioned at 50% RH. The results would disagree by 50% or more. | Feature | ASTM D618-21 | ISO 291
Accreditation bodies (A2LA, UKAS, NABL) now reference D618-21. If your quality manual says "D618-13," you are non-conforming. Comparing ASTM D618-21 to ISO 291 If you work globally, you may know ISO 291:2008 ( Plastics – Standard atmospheres for conditioning and testing ). The two are technically harmonized but not identical.
No. "Laboratory ambient" varies daily. D618-21 requires a controlled chamber, not a room air conditioner. While the standard is reaffirmed periodically, the 2021
ISO 291 is more forgiving on humidity tolerance but requires longer conditioning. ASTM D618-21 is stricter on RH but shorter on time. Never assume compliance with one means compliance with the other. 10 Frequently Asked Questions (FAQ) Q1: Can I get ASTM D618-21 for free? A: Not legally unless your employer subscribes to ASTM Compass or you have academic access.