ASTM D570 Water Absorption of Plastics

Scope

ASTM D570 applies to rigid and semi-rigid plastics in the form of molded or machined test specimens. The standard specifies multiple test conditions — immersion temperature, immersion duration, and pre-conditioning procedure — that are selected based on the material type and the intended application of the data. The result in each case is the percentage increase in mass relative to the conditioned dry mass, calculated from the before-and-after weighings.

Test conditions defined within the standard include:

• 24-hour immersion at 23°C — the standard short-term condition used for general material comparison and datasheet reporting
• Immersion to equilibrium at 23°C — extended immersion continued until mass gain stabilizes, representing the maximum absorption the material will reach under ambient temperature water exposure
• Immersion at 50°C — an accelerated condition used to estimate long-term absorption behavior more rapidly than equilibrium testing at 23°C permits
• 2-hour immersion in boiling water — severe conditioning used to assess absorption under aggressive thermal and aqueous exposure, or to evaluate materials intended for high-temperature water contact service
• Long-term immersion variations — as specified in applicable product standards or customer requirements for specific end-use simulations

Applications

• Material selection and comparison — ranking candidate materials by water absorption to identify grades with the lowest moisture sensitivity for humid or wet service environments
• Datasheet characterization — generating the water absorption value reported on material datasheets and in material property databases under standardized 24-hour and equilibrium conditions
• Dimensional stability assessment — supplying absorption data as an input to dimensional change calculations for components with tight tolerances in humid or wet environments
• Electrical insulation qualification — evaluating moisture-induced degradation of dielectric properties for electrical and electronic enclosures, connectors, and insulation components
• Food contact and medical device compliance — assessing water absorption behavior as part of material approval programs for applications involving sustained contact with aqueous media
• Quality control and incoming inspection — verifying that production lots and incoming raw materials meet specified absorption limits before processing or use
• Formulation and compound development — quantifying the effect of resin grade, filler type, coupling agent, or moisture stabilizer additions on the absorption behavior of a compound relative to the base resin

Benefits

• Universal applicability — the method applies to the full range of thermoplastic, thermoset, filled, and unfilled plastic materials, making it the single most widely used absorption characterization method for plastics
• Multiple test conditions in one standard — 24-hour, equilibrium, elevated temperature, and boiling water conditions are all defined within ASTM D570, allowing the appropriate condition to be selected for the application without referencing multiple standards
• Simple, accessible procedure — the test requires only a precision balance, a temperature-controlled water bath, and a drying oven, making it practical for quality control laboratories without specialized equipment
• Direct input to material selection and design — the percentage absorption value feeds directly into swelling calculations, property retention assessments, and comparative material rankings used in design and specification decisions
• Lot-to-lot quality verification — absorption is sensitive to changes in resin molecular weight, filler content, moisture stabilizer concentration, and processing history, making it a useful indicator of material consistency across production lots
• Supports accelerated aging programs — elevated-temperature and boiling-water conditions provide accelerated estimates of long-term moisture uptake behavior, reducing the time required to generate service-relevant data.