Hydrophobicity testing standards define the standardized laboratory and field methods used to measure how effectively a material repels water, expressed through contact angle values, hydrophobicity classes, or spray ratings. This article reviews the major international standards—including IEC TS 62073, ISO 4920, ISO 811, and the EN 13579/13580 series—covering sample types, test items, measurement procedures, and industrial applications for materials such as silicone rubber insulators, technical textiles, coatings, and construction products.
Technical Overview
Hydrophobicity describes the ability of a solid surface to resist wetting by water. In quantitative terms, a surface is generally classified as hydrophilic when the static water contact angle is below 90 degrees, hydrophobic at or above 90 degrees, and superhydrophobic at or above 150 degrees combined with low contact angle hysteresis. Because water films on material surfaces can trigger leakage currents, flashover, corrosion, icing, and substrate deterioration, hydrophobicity is a critical quality and performance attribute across the electrical power, textile, coating, and construction industries.
Hydrophobicity testing standards harmonize how this property is measured and reported. The most widely applied framework for electrical insulation is IEC TS 62073, which specifies both a static contact angle (SCA) method and a spray method with a seven-level classification (HC1 to HC7). For fabrics, ISO 4920 and JIS L 1092 establish spray rating methods, while ISO 811 and ISO 9865 address water penetration under hydrostatic pressure and simulated rainfall, respectively. For hydrophobic impregnations on concrete, EN 13579 and EN 13580 define drying behavior, water absorption, and penetration depth. National frameworks such as the GB/T series in China largely align with these IEC and ISO methodologies, and all procedures referenced here can be performed by accredited third-party laboratories.
Testing Samples
Polymeric Insulation Materials
Silicone rubber and EPDM housings, sheds, and complete composite insulators used on overhead transmission and distribution lines are the most common samples. Test pieces may be cut from finished products, molded from the same compound, or taken as in-service specimens during condition assessment, since the hydrophobicity of polymer surfaces degrades under corona discharge, UV exposure, and pollution deposition over time.
Textiles and Technical Fabrics
Water-repellent finished woven, knitted, and nonwoven fabrics—such as outdoor apparel materials, tent fabrics, filtration media, and protective clothing—are tested to verify the durability and uniformity of repellent finishes after washing, abrasion, or weathering.
Coatings and Surface Treatments
Protective coatings, nanocoatings, anti-graffiti systems, self-cleaning architectural coatings, and glass treatments are evaluated to confirm that the applied layer delivers the intended water-beading behavior on metal, glass, ceramic, or polymer substrates.
Construction Materials
Concrete, natural stone, brick, and masonry specimens treated with hydrophobic impregnation agents are tested in accordance with the EN 13579 and EN 13580 framework to quantify water absorption reduction and treatment penetration depth.
Films and Packaging Materials
Plastic films, corona-treated packaging webs, and barrier layers are assessed using contact angle methods such as ISO 15989 to characterize surface energy, printability, and wetting behavior.
Testing Items
Typical test items specified in hydrophobicity testing standards include:
- Static water contact angle (SCA) measurement
- Dynamic contact angle and contact angle hysteresis (advancing and receding angles)
- Sliding or rolling angle of a water droplet
- Hydrophobicity classification HC1 to HC7 by the spray method
- Spray rating for textiles (for example, ISO 4920 scale from 100, indicating no surface wetting, down to 0, indicating complete wetting)
- Resistance to water penetration under hydrostatic pressure
- Water absorption by immersion or boiling, expressed as percentage mass change
- Hydrophobicity transfer through a pollution layer (specific to silicone rubber)
- Hydrophobicity recovery after artificial corona, UV, or contamination aging
- Water absorption reduction and penetration depth for hydrophobic impregnations on concrete
Testing Methods
Static Contact Angle Method
A droplet of deionized water of defined volume—typically a few microliters—is deposited on the specimen surface using a micro-syringe or automated dosing system. The tangent angle at the three-phase contact line is measured with a goniometer and imaging software. IEC TS 62073 specifies this method for insulator surfaces, while ASTM D7334 and ISO 15989 cover coatings and plastic films, respectively. Multiple droplets are measured at distributed points, and the mean and standard deviation are reported together with the resulting classification.
Spray Method and HC Classification
Per IEC TS 62073, a fine water spray is applied to the surface from a defined height and volume. The resulting droplet pattern is compared visually or by image analysis against standardized reference photographs, producing a classification from HC1 (strongly hydrophobic, small discrete beads) to HC7 (hydrophilic, continuous water film). This method is fast, suitable for field use, and widely applied to in-service composite insulators; results of HC1 to HC2 indicate excellent water-repellent condition, while HC5 and above signal significant loss of hydrophobicity and increased pollution flashover risk.
Spray Rating Test for Textiles
ISO 4920 and the spray method within JIS L 1092 apply a standardized water shower to a fabric mounted at a fixed angle and then compare the wetted pattern against rating standards. A rating of 100 means no sticking or wetting of droplets, and lower ratings reflect progressive wetting of the specimen face. The test is often repeated after laundering or abrasion cycles to assess repellency durability.
Water Penetration Resistance
ISO 811 subjects fabric specimens to steadily increasing hydrostatic pressure on one face until water penetrates to the third position, reporting the pressure in kilopascals or centimeters of water column. ISO 9865, the rain shower (Bundesmann-type) test, exposes the fabric to simulated rainfall while measuring water penetration and water absorbed by the fabric, making it suitable for evaluating finished weatherproof assemblies.
Water Absorption and Impregnation Performance
For polymeric materials, specimens are immersed or boiled for a defined period and the percentage mass increase is calculated; low values confirm low water uptake. For concrete protection, EN 13580 measures the reduction in capillary water absorption achieved by a hydrophobic impregnation and verifies treatment depth, while EN 13579 evaluates the drying behavior of impregnated concrete. ISO 62 and ASTM D570 provide parallel water absorption procedures for plastics.
Hydrophobicity Transfer and Recovery Tests
Unique to silicone rubber, hydrophobicity transfer is evaluated by applying a defined pollution layer (such as a slurry of inert powder and salt) to the surface and periodically measuring the contact angle or HC class of the polluted layer over time. Recovery testing measures how quickly a surface regains hydrophobicity after temporary degradation by corona or severe wetting, both of which are key selection parameters under IEC 60815 and material qualification under IEC 62217.
Applications
Hydrophobicity testing standards support critical engineering and procurement decisions in many sectors:
- Electric power systems: incoming inspection and routine condition assessment of composite insulators on overhead lines and substations, where retained hydrophobicity suppresses leakage current and pollution flashover
- Outdoor and technical textiles: qualification of durable water repellent finishes for rainwear, tents, military and medical protective fabrics
- Building protection: verification of hydrophobic impregnations on bridge decks, facades, and historic masonry to reduce chloride ingress and freeze-thaw damage
- Coatings and surface engineering: development and quality control of self-cleaning, anti-icing, anti-corrosion, and easy-clean coatings
- Packaging and printing: surface energy mapping of films to confirm wettability for adhesives, inks, and laminating processes
- Automotive, aviation, and wind energy: assessment of water-repellent and anti-icing treatments on glass, rotor blades, and sensor surfaces
FAQ
What is the difference between hydrophobic and superhydrophobic surfaces?
A hydrophobic surface has a static water contact angle of 90 degrees or greater, while a superhydrophobic surface achieves at least 150 degrees with low hysteresis, causing droplets to roll off easily. Superhydrophobicity usually requires combined micro- and nano-scale surface roughness together with low surface energy chemistry.
What do hydrophobicity classes HC1 to HC7 mean?
Defined in IEC TS 62073, HC1 represents a strongly hydrophobic surface covered with small discrete water beads, and HC7 represents a fully wetted, hydrophilic film. Classes are assigned by comparing sprayed droplet patterns with reference images or by correlating contact angle ranges.
Which standard applies to textile water repellency testing?
ISO 4920 and JIS L 1092 specify the spray rating method for surface wetting resistance, while ISO 811 and ISO 9865 evaluate resistance to water penetration under hydrostatic pressure and rainfall. Selection depends on whether surface beading or penetration resistance is the performance requirement.
How are specimens prepared and conditioned before testing?
Specimens are cleaned according to the standard protocol to remove dust, oils, and release agents, then conditioned in a standard laboratory atmosphere, typically 23 degrees Celsius and 50 percent relative humidity, before contact angle, spray, or absorption measurements are taken.
Can hydrophobicity be tested on installed equipment in the field?
Yes. The IEC TS 62073 spray method was designed for on-site use, allowing maintenance crews to classify insulator surfaces directly on energized-adjacent or de-energized assets using portable spray bottles and reference classification charts or image capture devices.
Why is hydrophobicity transfer testing important for silicone rubber?
Silicone rubber can restore hydrophobicity to pollution layers deposited on its surface by migration of low molecular weight siloxanes. Transfer testing quantifies this self-restoring capability, which is the primary reason silicone composite insulators outperform porcelain and glass in heavily polluted environments.