Waiting for up to 100 days for a sample to be ready is often impractical for routine manufacturing or quality control. Therefore, the standard makes a critical distinction: the conditioning procedures prescribed are designed to obtain in a reasonable timeframe, not necessarily to achieve complete equilibrium.
This is the most widely referenced procedure in plastics testing. It establishes the baseline "Standard Laboratory Atmosphere." 23 ± 2°C (73.4 ± 3.6°F) Relative Humidity (RH): 50 ± 10%
Global manufacturers frequently juggle American (ASTM) and European/International (ISO) standards. The ISO equivalent to ASTM D618 is ( Plastics — Standard atmospheres for conditioning and testing ). While they share the same goal, key differences exist: ASTM D618-21 Standard Atmosphere 23 °C / 50% RH 23 °C / 50% RH (or 27 °C / 65% RH for tropical zones) Temperature Tolerance ± 2 °C (Standard) Class 1: ± 1 °C / Class 2: ± 2 °C Humidity Tolerance Class 1: ± 5% RH / Class 2: ± 10% RH Procedure Variety Includes specific thermal steps (Procedures B-F) Focuses primarily on atmospheric classes
is a standard practice created by ASTM International that defines the necessary environmental conditions and procedures for conditioning plastic materials prior to testing.
: Eliminating the influence of a material's previous exposure history (such as storage in a hot warehouse or damp basement) so that tests are consistent. Predictive Testing
Standard Practice for Conditioning Plastics for Testing - ASTM
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Because plastics can absorb moisture or change properties based on ambient conditions, testing them immediately after manufacturing or in varying ambient conditions leads to inconsistencies.
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Plastics are highly sensitive to their surroundings. Unlike metals, polymers absorb moisture from the air and expand or contract significantly with temperature shifts. The Impact of Humidity
Details the required equipment:
ASTM D618-21 establishes standard procedures for conditioning plastic specimens to ensure reproducible test results by controlling temperature and humidity, with Procedure A commonly requiring 40-88 hours at 23°C and 50% relative humidity. This practice is essential for stabilizing physical and electrical properties across various lab environments. The official standard can be purchased and downloaded at ASTM International .
