Water Repellency Test

Water Repellency Test – Standardized Evaluation of Surface Resistance to Wetting for Textiles, Leather, and Building Materials

As an ISO/IEC 17025 accredited (CNAS) independent laboratory, we provide professional water repellency testing services for manufacturers, importers, and quality assurance teams in Angola. Water repellency is the ability of a material surface to resist wetting by water, causing water droplets to bead up and roll off rather than spreading or being absorbed. This property is essential for outdoor apparel, workwear, umbrellas, tents, footwear, geotextiles, protective covers, and construction membranes. Unlike waterproofness (which prevents water penetration under pressure), water repellency focuses on the surface’s initial resistance to wetting, often imparted by durable water repellent (DWR) finishes, waxes, silicones, or fluorocarbon coatings. Our laboratory performs standardized spray tests, contact angle measurements, and rain simulation tests (Bundesmann) to quantify repellency, verify finishing consistency, and assess durability after laundering or abrasion. Results help clients ensure that their products perform effectively in Angola’s rainy and humid conditions – from coastal downpours to highland mist – and meet international specifications for protective and outdoor gear.

Types of Samples We Test for Water Repellency

• Rainwear fabrics (jackets, pants, coveralls) for construction, mining, and agriculture workers
• Umbrella and parasol fabrics (polyester, nylon, pongee, with DWR finish)
• Tent and tarpaulin materials (coated polyester, cotton canvas, silicone‑impregnated nylon)
• Footwear upper materials (leather, suede, synthetic leather, textile mesh)
• Work gloves and protective clothing (treated cotton, aramid blends, coated fabrics)
• Geotextiles and erosion control blankets (woven and nonwoven)
• Automotive interior textiles (seat fabrics, carpet, convertible tops)
• Leather goods (bags, belts, saddlery, upholstery)
• Building materials (breathable membranes, house wraps, roofing underlayment, plaster mesh)
• Finished consumer products (backpacks, outdoor furniture covers, PPE covers)

Fundamental Principles – Static vs. Dynamic Water Repellency

Water repellency can be evaluated under static conditions (water drops placed on the surface) or dynamic conditions (water spray or rain). The key parameters measured include:

• Spray rating (0–100) – Visual rating of the surface after a standardized water spray. Higher numbers indicate better repellency.
• Contact angle (θ) – Angle between the water droplet and the solid surface; θ > 90° indicates repellency, θ > 150° indicates superhydrophobicity.
• Rain penetration (g) – Mass of water passing through the specimen during simulated rainfall.
• Water absorption (%) – Increase in specimen mass after water exposure, relative to dry weight.

The tests are performed after conditioning (23°C ± 2°C, 50% ± 5% RH) to ensure that moisture from storage does not affect results. For products intended to be washed or used in the field, we also test after accelerated laundering, dry cleaning, or abrasion cycles to evaluate durability of the water‑repellent finish.

Standard Test Methods for Water Repellency

Our laboratory follows internationally recognized test methods, each suitable for different material types and performance requirements.

1. Spray Rating Test (Static Spray – Fabric Surface)

This is the most widely used screening test for water repellency of textile fabrics, including finished garments and raw materials.

• Equipment – Spray rating tester: a funnel with a standard spray nozzle (15 holes, 0.5 mm diameter) mounted 150 mm above the specimen, which is held at 45°.
• Procedure – 250 mL of distilled water (20°C ± 2°C) is poured into the funnel, spraying onto the specimen in approximately 25–30 seconds. The specimen is then gently tapped and compared to standard reference images showing various degrees of wetting.
• Rating scale – 100 = no sticking or wetting; 90 = slight random sticking; 80 = water beading at spray points; 70 = partial wetting; 50 = complete wetting; 0 = complete wetting of entire surface.
• Reporting – Average rating from at least 3 specimens. Typical acceptable rating for outdoor garments is ≥ 80 (or ≥ 70 for less demanding applications).

2. Bundesmann Rain Test (Dynamic Rain Simulation)

This test simulates walking rain, where the fabric is subjected to water pressure, rubbing, and movement.

• Equipment – Bundesmann rain tester: rotating specimens under a controlled rain shower (typically 65 mm/h or 100 mm/h intensity) with a rubbing arm that contacts the back of the fabric.
• Duration – Standard 10 minutes; can be extended for heavy‑rain simulation.
• Measurements – After the test, we collect and weigh: (a) water that has penetrated through the fabric, (b) water absorbed by the fabric, and (c) we note the appearance of the fabric (beading, wetting, dripping).
• Interpretation – Low penetration (e.g., < 5 g) and low absorption (e.g., < 10%) indicate excellent dynamic water repellency. The test is highly relevant for outerwear and protective covers.

3. Contact Angle Measurement (Quantitative Surface Analysis)

For precise, numerical evaluation of repellency, especially for coatings, films, and smooth surfaces.

• Equipment – Goniometer with high‑resolution camera and automated droplet dispenser.
• Procedure – A 2–5 µL droplet of distilled water is placed on the specimen surface. After stabilization (2 seconds), the droplet profile is captured and the contact angle is calculated using the Young‑Laplace or tangent method.
• Variants – We can also measure advancing and receding angles (hysteresis) by adding or withdrawing liquid. A low hysteresis (< 10°) indicates easy droplet roll‑off.
• Typical values – Untreated cotton: ~0° (absorbs); standard DWR: 110°–120°; silicone treatment: 100°–110°; superhydrophobic coating: >150°.

4. Water Absorption (Gravimetric) Test – Static Immersion

Used for materials where long‑term water contact is expected (e.g., geotextiles, leather, canvas).

• Procedure – A weighed specimen is placed on the surface of distilled water (or fully immersed) for a specified time (1 hour, 24 hours). It is then blotted to remove surface droplets and reweighed.
• Calculation – Water absorption (%) = (Wet weight – Dry weight) / Dry weight × 100.
• Acceptance – For water‑repellent leather, absorption < 20% after 24 hours is typical; for highly repellent textiles, absorption < 5%.

5. Hydrostatic Pressure Test (Waterproofness – Combined with Repellency)

While not purely a repellency test, it is often requested for rainwear and protective clothing to establish the pressure resistance of the material after the surface repellency is overcome.

• Procedure – The specimen is clamped over a water reservoir. The water pressure is increased at a constant rate (e.g., 10 cm H₂O/min) until three droplets appear on the surface. The pressure at the third drop is recorded in mm H₂O or kPa.
• Interpretation – Higher hydrostatic pressure indicates better waterproofness, which complements water repellency. For a garment to be considered “waterproof”, values typically exceed 800 mm H₂O for light rain and 2000 mm H₂O for heavy rain.

Durability of Water Repellency – After Wash and Abrasion Testing

Many water‑repellent finishes are not permanent and degrade with laundering, dry cleaning, or mechanical wear. We offer optional pre‑conditioning to simulate service life.

• Laundering cycles – Specimens are washed in a standard domestic washing machine using a reference detergent, at 40°C or 60°C, for a specified number of cycles (e.g., 5, 10, 20 washes). After washing, they are line‑dried or tumble‑dried according to the product’s care label. Then the water repellency (spray rating) is re‑measured. The number of cycles after which the rating falls below the acceptance threshold is reported as the “durability” of the finish.
• Dry cleaning cycles – For garments labeled “dry clean only”, we simulate dry cleaning using perchloroethylene or hydrocarbon solvent.
• Abrasion cycles – Using a Martindale or Taber abrader, we subject the specimen to a specified number of rubbing cycles (e.g., 1000, 5000 cycles) before measuring water repellency. This simulates wear at high‑friction areas (elbows, knees, seat).
• UV aging – Exposure to xenon arc or UV fluorescent lamps (200–500 hours) followed by repellency testing quantifies the effect of sunlight.

Factors Influencing Water Repellency Test Results

• Fabric construction – Tight weaves, high yarn density, and fine fibers promote water beading and reduce penetration.
• Fiber type – Polyester and nylon have higher inherent repellency than cotton, wool, or rayon.
• Finish quality and application – Uniform, properly cured DWR finishes give high and consistent repellency. Over‑application can cause stiffness; under‑application leads to patchy repellency.
• Surface contamination – Oils, dirt, fabric softeners, and residual processing chemicals lower repellency by reducing surface tension.
• Water temperature and purity – Cold distilled water gives the most consistent results; tap water or warm water can introduce variability.
• Specimen orientation – Directional fabrics (e.g., corduroy, rib knits) may show different repellency when tested along vs. across the direction.
• Handling – Touching the test area with bare hands transfers skin oils, reducing measured repellency.

Quality Control and Acceptance Criteria

• For routine production control, we test 3 to 5 specimens per batch. The acceptable minimum spray rating is agreed with the client (e.g., ≥ 80 for premium rainwear, ≥ 70 for general workwear).
• For the Bundesmann test, typical acceptance criteria: penetration < 10 g, absorption < 15% after 10 minutes of rain at 65 mm/h.
• For contact angle, a minimum of 110° is often required for DWR‑treated fabrics.
• When comparing two production runs or different suppliers, we use a two‑sample t‑test to determine if the difference in average spray rating is statistically significant (p < 0.05).

Reporting and Deliverables

Each water repellency test report includes the following information:

• Sample identification (material composition, construction, finish type, batch number, pre‑treatment history – washes, abrasion, UV)
• Test method used (spray rating, Bundesmann, contact angle, absorption, hydrostatic pressure) with detailed parameters (water temperature, exposure time, rain intensity)
• Conditioning conditions (temperature, humidity, time)
• Individual results for each specimen and each direction (if applicable)
• Statistics: average, standard deviation, coefficient of variation
• For durability tests: results before and after treatment (e.g., spray rating after 5 washes)
• Photographs (upon request) of the specimens after the spray test or contact angle images
• Comparison with client‑supplied specification (if provided) – pass/fail statement
• Raw data (spray rating reference images, contact angle calculation logs) archived for 10 years

No statement of compliance with any external standard or regulation is made unless the client has provided specific acceptance criteria in writing. The report is intended for material qualification, production quality control, and supplier validation.

Practical Applications for Angolan Industries

• Rainwear for construction and mining: Ensuring that jackets and pants maintain spray rating ≥ 80 after 5 washes.
• Geotextiles for drainage: Verifying that erosion control blankets do not become waterlogged, which would increase weight and reduce effectiveness.
• Umbrella manufacturing: Testing fabric repellency to prevent water soaking through after heavy use.
• Automotive seat fabrics: Evaluating repellency after abrasion to ensure that spills and rain do not permanently stain the upholstery.
• Leather goods: Measuring water absorption to ensure that bags and belts do not become heavy or deformed after exposure to rain.