The standard outlines several specific procedures (A through E) tailored to different material types and testing requirements. Conditioning Environment Primary Use Case 40 hours ( thick) or 88 hours ( Standard laboratory atmosphere for general testing. Procedure B in an oven 48 hours, followed by cooling in a desiccator Accelerated drying and thermal conditioning. Procedure C distilled water

While is the technically equivalent international standard, there are notable differences:

: Labs must utilize calibrated environmental chambers , circulating-air ovens, and precision hygrometers to verify conditions. ASTM D618 vs. ISO 291

: Provide a universal language for describing how specimens were handled prior to testing. Standard Conditioning Procedures

Conditioning is rarely about reaching "perfect" equilibrium, as some plastics might require 20 to 100 days to fully stabilize. Instead, ASTM D618-21 provides a practical framework to:

: Establish a consistent baseline so that results from one lab can be reliably compared to another.

: Variations are strictly limited. For example, if a temperature tolerance of is required, the humidity tolerance must be within

The "21" in the designation indicates that the most recent major revision was approved in . You can view or purchase the official document at the ASTM International website or through authorized distributors like the ANSI Webstore and Accuris Standards Store . Core Significance and Purpose

: Predict how a material will perform under specific "abnormal" conditions, such as extreme heat or high humidity.