Testing Methods for Fabric Water Absorbency Testers

Fabric water absorbency is one of the key indicators of textile functionality, directly impacting critical applications such as the comfort of clothing, the safety of medical dressings, and the performance of outdoor sports equipment.

Fabric water absorbency refers to a fabric’s ability to absorb liquid water, typically characterized by metrics such as absorption rate, water absorption capacity (amount of water absorbed), and capillary rise height. Different application scenarios have varying requirements for water absorbency:

1. Towels and bath towels require high water absorbency and rapid absorption, with a primary focus on settling time and water absorption capacity;

2. Quick-dry sports fabrics require rapid moisture absorption and diffusion, with emphasis on droplet spread time and capillary rise;

3. Medical dressings require moderate water absorption and good liquid retention capacity;

4. Outdoor waterproof fabrics, conversely, require low water absorption and high water repellency;

5. Products such as diapers and sanitary napkins require high water absorption and low reverse permeation.

1. Drop Absorption / Sinking Time Method

The drop absorption method is one of the most classic and commonly used methods for testing fabric water absorption. It works by measuring the time it takes for a water droplet to fully penetrate the fabric (or for the fabric to begin sinking) from the moment it comes into contact with the fabric surface; the shorter the time, the better the water absorption.

Applicable standards primarily include GB/T 22799-2019 “Test Method for Water Absorbency of Towel Products” (Method A), as well as the internationally recognized AATCC TM79 “Water Absorbency of Textiles.”

Test Procedure: First, allow the test specimen to reach moisture equilibrium under standard atmospheric conditions for at least 4 hours; then lay the specimen flat on the test bench with the tip of the burette positioned 10 mm above the specimen’s surface; release a standard volume (typically 0.05 mL) of water, and start the timer simultaneously; record the time at which the specular reflection of the water droplet completely disappears, i.e., the water absorption time; each sample must be tested 5 to 10 times at different locations, and the average value is taken as the final result.

Regarding result evaluation, high-quality towels typically have a settling time of less than 15 seconds, while qualified products generally have a settling time of less than 60 seconds. If the time exceeds 90 seconds, it may indicate excessive water-repellent finishing or issues with the fiber structure. The instruments suitable for this method primarily include the drop-test water absorption tester and the towel water absorption tester.

2. Absorption Method (Absorption Gravimetric Method)

The absorption method calculates the water absorption rate—the percentage of water absorbed relative to the original weight—by measuring the change in mass of the fabric before and after water absorption. The formula is: Water Absorption Rate = (Mass of Sample After Water Absorption - Mass of Dry Sample) / Mass of Dry Sample × 100%.

Applicable standards include GB/T 22799-2019 Method B, ASTM D4772 “Standard Test Method for Water Absorption and Drying of Textile Fabrics,” and ISO 9073-6 “Textiles—Determination of Water Absorption of Fabrics.”

Taking GB/T 22799 Method B as an example, the testing procedure is as follows: After the sample has been washed, dried, and conditioned, testing is conducted under standard conditions; 50 mL of water is passed through the sample via a standard funnel within 8.0 seconds; the unabsorbed water is collected, and the change in mass of the water basin before and after the test is measured; the water absorption rate is then calculated. This method specifies clear equipment requirements: the funnel must have a capacity of 50 mL, the flow rate must ensure that 50 mL of water passes through within 8.0 seconds, the waterproof circular ring must have a diameter of 150 mm, and the electronic balance must have a precision of 0.01 g.

3. Wicking Method (Capillary Rise Method)

The wicking method utilizes capillary action to measure the height to which a liquid rises through the gaps between fibers in a fabric. It is used to evaluate a fabric’s water-conducting capacity and water absorption and diffusion properties.

Applicable standards include AATCC TM197 “Textiles—Vertical Wicking: To a Specified Height,” AATCC TM198 “Textiles—Horizontal Wicking,” AATCC TM213 “Textiles—Vertical Wicking: To a Specified Time,” and GB/T 21655.1-2008 “Textiles—Evaluation of Moisture Absorption and Quick-Drying Properties.”

The vertical capillary rise test procedure is as follows: Cut the test specimen into a 25 mm × 200 mm strip and suspend it vertically on a test frame; immerse the bottom of the specimen in water to a depth of approximately 10 to 15 mm; record the height of the water mark at specified time intervals (5 minutes, 10 minutes, 15 minutes, 30 minutes); the capillary rise rate is calculated as the height of the rise divided by the elapsed time.

For horizontal wicking (droplet diffusion method), the fabric is laid flat on a horizontal platform, and a standard droplet is applied. The time required for the water to diffuse from the center to a specified diameter (e.g., 100 mm) is recorded; a shorter time indicates better horizontal diffusion performance. A higher wicking height indicates better water conductivity of the fabric. This method is particularly suitable for evaluating moisture-wicking and quick-drying properties in sports fabrics and functional underwear.

4. Dynamic Moisture Management Test (Moisture Management Test)

The dynamic moisture management test uses a multi-sensor system to simultaneously monitor the entire process of wetting, absorption, diffusion, and penetration of liquid water on both the front and back surfaces of the fabric, generating a comprehensive moisture management index.

Applicable standards include AATCC TM195 “Moisture Management Performance of Textiles” and GB/T 21655.2-2019 “Textiles—Evaluation of Moisture Absorption and Quick-Drying Performance.”

Test metrics include wetting time (the time from when the droplet contacts the surface until absorption begins; an excellent standard is less than 3 seconds), absorption rate (the amount of water absorbed per unit time; higher is better), diffusion diameter (the range of moisture diffusion across the surface; larger is better), and unidirectional transfer index (the ability of moisture to transfer from the inner side to the outer side; an excellent standard is greater than 100%). Instruments suitable for this method include dynamic moisture management testers such as the SDL Atlas MMT and the DaRong Instruments TF128.

5. Spray and Rain Tests

Although the spray and rain tests are primarily used to evaluate water repellency, they complement water absorption tests and together form a comprehensive system for assessing the water performance of fabrics.

The spray test, based on AATCC TM22 and GB/T 4745, involves spraying 250 mL of water at a 45-degree angle, with results rated on a scale of 1 to 5. The rain test, in accordance with AATCC TM35, simulates heavy rain impact and determines water permeability by measuring the weight gain of absorbent paper. The Hydrostatic Pressure Test, in accordance with AATCC TM127 and GB/T 4744, determines the water resistance value by gradually increasing water pressure until water seeps through.

GB/T 22799-2019 “Test Methods for Water Absorbency of Towel Products,” which employs the sedimentation method and absorption method, is applicable to all types of woven towel products;

GB/T 21655.1-2008 “Evaluation of Moisture Absorption and Quick-Drying Properties of Textiles,” which employs a combined test method (wicking, water droplet diffusion, and drying rate), is applicable to moisture-absorbing and quick-drying textiles;

GB/T 21655.2-2019 “Evaluation of Moisture Absorption and Quick-Drying Properties of Textiles,” which employs the dynamic moisture transfer method and applies to knitted, woven, and nonwoven fabrics;

AATCC TM79 “Absorbency of Textiles,” which employs the sedimentation method and applies to general-purpose textiles;

AATCC TM197 “Vertical Wicking,” which employs the wicking height method and applies to water-conductive fabrics;

ASTM D4772 “Water Absorption and Drying of Fabrics,” using the gravimetric method, applicable to all types of fabrics;

ISO 9073-6 “Water Absorption of Textile Fabrics,” using the standard drop method, applicable to woven, knitted, and nonwoven fabrics;

JIS L 1907 “Testing of Water Absorption of Textiles,” using the drop diffusion method, applicable to textiles for the Japanese market.

Sample Pretreatment

All test specimens must be conditioned to achieve moisture equilibrium in standard atmospheric conditions (20±2°C, 65±4% RH) for at least 4 hours; otherwise, data deviations may exceed 15%. Before testing, remove impurities such as sizing agents and oils from the fabric surface, and avoid sampling from fabric edges or creased areas.

In the droplet method, the distance between the tip of the burette and the sample surface must be strictly uniform (typically 10 mm); variations in height will result in differences in the impact force of the water droplets. In the capillary method, the immersion depth of the sample’s bottom must be consistent (10 ± 2 mm); excessive depth will cause changes in hydrostatic pressure above the liquid surface. In the weighing method, samples must be weighed immediately after water absorption to avoid errors caused by moisture evaporation.

Fluctuations in ambient temperature and humidity can cause variations in fiber moisture regain. The solution is to use a laboratory with controlled temperature and humidity. Insufficient sample representativeness can lead to high data variability; therefore, the number of tests should be increased to five or more. Inadequate instrument calibration can result in systematic errors; balances and flow meters must be calibrated regularly.

The technical content in this article references authoritative standards such as GB/T 22799-2019, the GB/T 21655 series, and AATCC TM79/TM195/TM197, and is intended solely for technical exchange.