Water absorption testing is a fundamental evaluation method that quantifies how much moisture a new material takes up under controlled immersion conditions, providing critical insight into its dimensional stability, mechanical performance, and long-term durability. This guide covers the applicable international and national standards, specimen requirements, test procedures, calculation methods, and typical applications for water absorption testing of advanced polymers, composites, ceramics, building materials, and other new materials.
Technical Overview
Water absorption testing measures the mass of water that a material absorbs when immersed in water under specified temperature and time conditions, expressed as a percentage of the dry specimen mass. For new materials such as engineering plastics, fiber-reinforced composites, technical ceramics, foams, and functional films, moisture uptake can plasticize the polymer matrix, reduce mechanical strength and glass transition temperature, degrade dielectric and insulation properties, and cause swelling, warping, or interfacial delamination. Water absorption data is therefore essential for material qualification, batch quality control, durability modeling, and product certification.
The core calculation used by virtually all major standards is expressed as follows: Water absorption (%) = (m2 - m1) / m1 x 100, where m1 is the conditioned dry mass of the specimen and m2 is the mass measured after immersion, following removal and blotting of surface water.
The most widely applied standards frameworks include:
- ISO 62 and GB/T 1034 for water absorption of plastics
- ASTM D570 for water absorption of plastics by immersion
- ISO 10545-3 and GB/T 3810.3 for water absorption of ceramic tiles
- ASTM C373 for fired ceramic whiteware materials
- ASTM D2842 and ISO 2896 for rigid cellular plastics and foams
- ASTM D5229/D5229M for moisture absorption of polymer matrix composites
- ASTM C642 for absorption and voids in hardened concrete
- ASTM C1585 and EN 1925 for capillary water absorption of concrete and natural stone
- JIS K 7209 for water absorption testing of plastics in the Japanese standard system
Testing Samples
Polymer and Composite Materials
Typical samples include engineering plastics such as PA6, PA66, PC, POM, ABS, PEEK, and polyolefins, as well as glass-fiber and carbon-fiber reinforced polymer composites, laminates, and adhesive systems. Highly hygroscopic materials such as nylon may absorb several percent of water at saturation, while polypropylene typically absorbs less than 0.1 percent, so the test protocol must match the expected absorption range.
Advanced Ceramics and Inorganic Non-Metallic Materials
Samples include ceramic tiles, technical ceramics, porous ceramics, glass-ceramics, and refractory products. Water absorption is a key classification parameter for tiles; for example, porcelain tiles are generally defined as having a water absorption of 0.5 percent or less under the ISO 13006 classification system. Absorption values also correlate with open porosity, stain resistance, and frost resistance.
Building and Construction Materials
Concrete, mortar, gypsum products, natural and engineered stone, cement boards, wood-based panels such as MDF and particleboard, and thermal insulation products including EPS, XPS, and rigid polyurethane foam are commonly tested. For boards and foams, thickness swelling and surface-cell correction factors may be evaluated alongside mass absorption.
Films, Coatings, and Functional New Materials
Barrier films, protective coatings, sealants, battery separator membranes, biodegradable plastics, hydrogels, and nanocomposites are tested to characterize moisture sensitivity, permeation-related performance, and environmental reliability. These materials often require extended conditioning or kinetic analysis rather than a single 24-hour measurement.
Testing Items
Depending on the material type and the governing standard, accredited third-party laboratories typically offer the following test items:
- 24-hour water absorption rate by standard immersion at 23 degrees Celsius
- Water absorption after immersion in boiling water, for example 2 hours for ceramics or 2 hours for plastics per ASTM D570
- Long-term immersion absorption and saturation (equilibrium) water absorption
- Moisture absorption kinetics, including moisture diffusion coefficient and time-to-equilibrium per ASTM D5229
- Apparent porosity, open pore volume, and bulk density by vacuum saturation or hydrostatic weighing
- Capillary water absorption coefficient and initial rate of absorption (sorptivity)
- Thickness swelling and dimensional change after water immersion
- Moisture content determination by oven drying or Karl Fischer titration
Testing Methods
Standard Immersion Method at 23 Degrees Celsius
Following ISO 62, ASTM D570, or GB/T 1034, specimens are first dried to constant mass in an oven, typically at 50 degrees Celsius for plastics or 105 degrees Celsius for ceramic and mineral materials, then cooled to room temperature in a desiccator and weighed to obtain the dry mass m1. Specimens are fully immersed in distilled or deionized water maintained at 23 degrees Celsius for 24 hours. Each specimen is then removed, and free surface water is quickly removed with a dry lint-free cloth within a defined time window before the wet mass m2 is recorded. The absorption percentage is calculated from the mass gain. Standard plastic specimens are typically discs of 50 millimeters diameter and 3 millimeters thickness, with a minimum of three specimens per sample.
Boiling Water Method
The boiling method accelerates pore filling and is specified for ceramics under ISO 10545-3, GB/T 3810.3, and ASTM C373, and as a short exposure option for plastics under ASTM D570 and ISO 62. Oven-dried specimens are immersed in water which is brought to boiling, typically maintained for 2 hours in the tile method or 5 hours under ASTM C373, followed by a controlled cooling period in the water. Combined with hydrostatic weighing, this method additionally yields apparent porosity, apparent relative density, and bulk density.
Vacuum Saturation Method
In the vacuum method, specimens are placed in a sealed vessel, evacuated to a specified residual pressure to extract air from open pores, and then flooded with water so that pores fill completely under atmospheric pressure. This approach is required for low-porosity products such as porcelain tiles under ISO 10545-3 and is used in ASTM C642 for hardened concrete to determine absorption, density, and void content. It provides the maximum theoretical water uptake of the interconnected pore structure.
Long-Term Immersion and Moisture Diffusion Kinetics
For structural composites and high-performance materials, ASTM D5229/D5229M governs the measurement of moisture absorption properties. Specimens are immersed or exposed at constant temperature and humidity and weighed at successive intervals until the rate of mass change falls below a defined threshold, establishing the equilibrium moisture content. Plotting mass gain against the square root of time allows Fickian diffusion analysis and calculation of the through-thickness moisture diffusivity, a key input for environmental durability modeling and design allowables.
Capillary Absorption Method
In partial-immersion capillary tests such as ASTM C1585 for concrete and EN 1925 for natural stone, only one face of the specimen contacts water. The mass gain per unit area is recorded over time, and the sorption coefficient is derived from the linear relationship with the square root of time. This method best represents service conditions involving rain, splashing, or ground moisture.
Applications
Water absorption test results support engineering decisions across many sectors where new materials are deployed:
- Automotive and electric vehicles: qualification of battery housings, connectors, sensors, and interior components where moisture affects dimensional tolerance and electrical reliability
- Aerospace: humidity conditioning and moisture allowables for carbon fiber composite structures and adhesives
- Electronics and semiconductors: moisture sensitivity evaluation of PCB base laminates, encapsulants, and molding compounds to prevent delamination during reflow soldering
- Construction and building products: tile classification, frost durability assessment, insulation performance verification, and compliance with structural material specifications
- Marine and outdoor infrastructure: long-term water exposure aging studies for coatings, composites, and adhesives
- Packaging: moisture barrier characterization of films and biodegradable materials
- Research and quality control: incoming material inspection, supplier comparison, formulation optimization, and accelerated aging programs
FAQ
Which water absorption standard applies to my material?
Plastics are generally tested to ISO 62, ASTM D570, GB/T 1034, or JIS K 7209; ceramic tiles to ISO 10545-3 or GB/T 3810.3; fired ceramics to ASTM C373; polymer composites to ASTM D5229; foams to ASTM D2842 or ISO 2896; concrete to ASTM C642; and stone to EN 13755 or EN 1925. The choice depends on the product specification, target market, and contractual requirements.
How are specimens prepared before testing?
Specimens are cut to the dimensions specified by the standard, edges are finished to remove damage, and specimens are conditioned to constant dry mass in an oven and then cooled in a desiccator. Laboratory conditioning atmospheres, where required, follow ISO 291 or ASTM D618, typically 23 degrees Celsius and 50 percent relative humidity.
What is the difference between the immersion and boiling methods?
The immersion method at 23 degrees Celsius reflects room-temperature exposure and is used for comparison and specification compliance. The boiling method drives water into open pores more rapidly and completely, making it suitable for porous ceramics and for estimating apparent porosity and related density parameters.
How long does water absorption testing take?
A standard 24-hour immersion test with drying typically requires two to four working days including conditioning. Boiling methods require several hours of active testing plus drying and cooling. Saturation and diffusion kinetics studies may run from several weeks to several months, depending on material thickness and permeability.
How many specimens are required?
Most standards require a minimum of three specimens per material for statistical validity, although product-specific standards such as tile or stone methods may specify whole units or fragments of a minimum mass. Accredited third-party laboratories can advise on the appropriate specimen count and geometry for a given standard.
Can results from different methods or laboratories be compared directly?
Only results obtained under identical specimen geometry, drying conditions, water temperature, and exposure time are directly comparable. Because absorption is strongly dependent on thickness and surface-to-volume ratio, comparisons should always cite the test method and specimen configuration alongside the reported percentage value.