Water Absorption Testing: Methods, Standards & Material Applications
Asphalt and bitumen chemical property testing per ASTM D36 and D92 at Infinita LabWhat Is Water Absorption?
Water absorption is the amount of water that a material takes up when immersed in water or exposed to humid environments over a defined period, expressed as a percentage increase in mass relative to the original dry mass. It is a fundamental physical property that governs a material’s dimensional stability, mechanical property retention, electrical insulation performance, and chemical durability in service environments where moisture exposure is expected.
Water absorption testing is applicable to plastics, elastomers, composites, ceramics, textiles, wood, and concrete — with specific test methods defined for each material class.
Why Water Absorption Testing Matters
Dimensional Stability
Water absorbed by hygroscopic polymers (nylons, polyurethanes, cellulosic composites) causes dimensional swelling — potentially exceeding dimensional tolerances in precision components. Understanding water absorption enables design with appropriate dimensional tolerances that account for wet equilibrium dimensions.
Mechanical Property Degradation
Absorbed water acts as a plasticiser in polyamides and polyurethanes — reducing glass transition temperature (Tg), tensile modulus, and yield strength. In composite materials, moisture reduces the fibre-matrix interfacial shear strength and promotes delamination through osmotic swelling. Water absorption data enables the prediction of wet mechanical properties and the design of appropriate conditioning procedures before mechanical testing.
Electrical Insulation Performance
Water dramatically reduces the electrical resistivity and dielectric strength of insulating polymers and composites. PCB substrates, encapsulants, and insulating coatings must have low water absorption to maintain electrical performance in humid environments.
Chemical Resistance and Hydrolytic Stability
Materials exposed to water long-term may undergo hydrolysis of ester, amide, or carbonate linkages — degrading molecular weight and mechanical properties. Water absorption testing combined with mechanical property measurement after immersion characterises hydrolytic stability.
Standard Test Methods for Water Absorption
ASTM D570 — Water Absorption of Plastics
The primary ASTM standard for plastic water absorption. Specimens are dried to constant mass, then immersed in distilled water at 23°C for 24 hours (short-term) or until equilibrium (long-term). After immersion, surface water is blotted and the specimen is immediately reweighed. Water absorption is reported as percentage mass increase.
Optional tests include: 2-hour boiling water immersion (higher temperature accelerates absorption toward equilibrium) and 48-hour immersion for comparison of slower-absorbing materials.
ISO 62 — Plastics Water Absorption
ISO 62 is the international equivalent, defining three methods: Method 1 (23°C, 24 h), Method 2 (50°C, until constant mass), and Method 3 (100°C, 30 min followed by weigh in immersed condition). Results are expressed as % mass increase.
ASTM C272 — Water Absorption of Sandwich Core Materials
Governing the testing of structural foam and honeycomb core materials (described in Blog 66 of Series 1).
ASTM D5229 — Moisture Absorption Properties of Composite Materials
Specifically governs moisture conditioning and absorption equilibrium determination for polymer matrix composite materials — used to condition composite specimens before mechanical testing to represent wet service conditions.
Equilibrium vs. 24-Hour Water Absorption
24-hour immersion provides an index of short-term moisture uptake — useful for comparative material screening and rapid quality verification. Equilibrium (saturation) water absorption — reached after weeks to months of immersion depending on specimen thickness and diffusivity — characterises the worst-case moisture content the material will reach in prolonged wet service.
For design purposes, both the rate of moisture uptake (diffusion coefficient) and the equilibrium content are needed. The Fickian diffusion coefficient is determined from the initial linear portion of the mass gain vs. √time plot.
Common Water Absorption Values for Engineering Materials
| Material | 24h Water Absorption (ASTM D570) |
| PTFE | <0.01% |
| Polypropylene | <0.02% |
| Polycarbonate | 0.15–0.18% |
| ABS | 0.3–0.4% |
| Nylon 6 | 1.6–1.9% |
| Nylon 66 | 1.0–1.3% |
| Polyurethane | 0.5–1.5% |
| Epoxy (cured) | 0.1–0.4% |
Industrial Applications
In electronics, PCB substrate water absorption is a critical specification — low water absorption materials (PTFE, modified epoxy laminates) are selected for high-frequency applications where moisture-induced dielectric constant increases would degrade signal integrity. In automotive, nylon 6 and nylon 66 components are conditioned to equilibrium moisture content before mechanical testing per SAE J1975 to provide design-relevant wet properties.
Why Choose Infinita Lab for Water Absorption Testing?
Infinita Lab provides ASTM D570, ISO 62, ASTM D5229, and ASTM C272 water absorption testing through our nationwide accredited materials testing laboratory network, supporting material selection, product qualification, and quality control programmes.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
Why must specimens be dried to constant mass before water absorption testing? Initial moisture content of as-received specimens varies with storage humidity history — affecting the baseline mass from which absorption is calculated. Drying to constant mass (typically 50°C for 24 hours per ASTM D570) establishes a reproducible, dry reference mass, ensuring that measured mass gains reflect only water absorption during the test.
What is the Fickian diffusion model for polymer water absorption? Fickian diffusion predicts that moisture uptake is initially linear with the square root of immersion time, then decelerates to equilibrium. The diffusion coefficient D (mm²/s) is calculated from the initial linear slope and specimen thickness. This model is valid for most homogeneous polymers — deviations indicate surface barrier layers, swelling-induced diffusion changes, or hydrolysis.
How does moisture absorption affect the mechanical properties of nylon components? Nylon absorbs 1–4% water at service humidity, which acts as a plasticiser — reducing tensile modulus by 30–50%, reducing yield strength by 20–30%, but increasing elongation at break. Dry-as-moulded nylon properties severely overestimate stiffness and strength for ambient humidity service. Conditioned (wet) properties from ASTM D638 after moisture equilibration provide the design-relevant mechanical data.
Can water absorption be used to detect contamination or incorrect material identity? Yes. Water absorption is sensitive to polymer type and filler content. A material that absorbs significantly more or less than the reference grade indicates either a different polymer identity, different filler system, or contamination. Combined with density and FTIR testing, water absorption provides a cost-effective incoming material verification battery.
What is the difference between water absorption and moisture regain in textile testing? Water absorption (ASTM D570) measures mass gain during immersion — the water taken up by immersion in liquid water. Moisture regain is the equilibrium moisture content at defined relative humidity (65% RH standard) — the moisture absorbed from the vapour phase. Both are relevant for textiles: absorption characterises wicking and wet feel; regain characterises the fibre's dimensional stability and electrostatic behaviour at ambient humidity.
