Oil repellency testing evaluates the ability of geomagnetic fabric—a functional textile embedded with magnetic fibers or particles—to resist wetting and penetration by oils and low-surface-tension hydrocarbons. Accredited third-party laboratories assess this performance using internationally recognized methods such as ISO 14419 and GB/T 19977, which assign a hydrocarbon resistance grade from 1 to 8. This article explains the applicable standards, sample requirements, test procedures, and quality criteria for geomagnetic fabric oil resistance evaluation.
Technical Overview
Geomagnetic fabric is a functional textile that incorporates magnetic fibers, magnetic particle composites, or magnetic coatings into woven or knitted structures. It is commonly used in wellness apparel, support garments, bedding, insoles, and healthcare-oriented products where a stable weak magnetic field is expected to be maintained close to the body. Because such products are routinely exposed to skin oils, cosmetics, cooking oils, and lubricants during service, manufacturers frequently apply durable water- and oil-repellent finishes, based on fluoropolymer or fluorine-free chemistries, to the fabric surface.
Oil repellency is a surface-energy-dependent property that can be influenced by fabric construction, magnetic particle loading, finish concentration, curing quality, and subsequent laundering or abrasion. Independent laboratory testing is therefore required to verify that the finished geomagnetic fabric achieves the intended oil repellency grade and retains it after simulated use. The internationally accepted approach is the hydrocarbon resistance test, in which a graded series of hydrocarbon liquids of progressively lower surface tension is applied to the fabric surface and the resistance to wetting is scored on a scale from 1 to 8.
Testing Samples
Finished Geomagnetic Fabric
Primary test specimens are cut from production batches of repellent-finished geomagnetic fabric. A minimum of three pieces, each approximately 30 cm x 30 cm and taken from different positions across the fabric width, is recommended to account for finish application variability. Specimens must be free of creases, contamination, and visible defects, and must be conditioned at 20 ± 2 °C and 65 ± 2 % relative humidity in accordance with ISO 139 before testing.
Durability Test Specimens
To evaluate retention of oil repellency, identical specimens are prepared after a defined number of laundering cycles (for example, 5, 10, or 20 domestic washes), after Martindale abrasion, or after both treatments. These conditioned specimens are then re-tested using the same hydrocarbon resistance method so that grade retention can be quantified.
Product-Level Specimens
When the test object is a finished article such as a magnetic support wrap, mattress underlay, or insole, specimens are cut directly from the functional zones of the product. Seams, labels, and non-representative areas are excluded, and the sample identity, color, and construction details are documented in the test report.
Testing Items
A typical scope of work for geomagnetic fabric oil repellency assessment includes the following items:
- Initial oil repellency grade by hydrocarbon resistance test (grade 0 to 8)
- Oil repellency grade after repeated laundering cycles
- Oil repellency grade after standardized abrasion or rubbing
- Static contact angle of reference oil droplets as supplementary surface-energy characterization
- Visual assessment of oil staining, halo formation, and penetration through the fabric
- Optional cross-check that the repellent finishing process has not degraded the surface magnetic induction strength of the fabric
Testing Methods
Hydrocarbon Resistance Test (ISO 14419 / GB/T 19977)
The principal method follows ISO 14419 (adopted in Europe as EN ISO 14419) and the Chinese national standard GB/T 19977. The conditioned specimen is placed on a smooth, horizontal surface over clean white absorbent paper. Starting with the lowest-grade oil, five small drops of approximately 5 μL each are gently placed on the fabric surface using a micropipette or dropper. After 30 seconds, each drop site is examined for wetting, indicated by loss of the domed drop shape, darkening of the fabric, or formation of a halo. If no wetting is observed at three or more of the five drop positions, the specimen passes that grade and the next higher-grade liquid is applied. The reported oil repellency grade is the highest numbered oil that does not wet the fabric.
The graded hydrocarbon series, listed from the easiest to the most difficult to repel, is as follows:
- Grade 1 – medicinal white mineral oil (surface tension approximately 30 mN/m)
- Grade 2 – 65/35 mixture of white mineral oil and n-hexadecane
- Grade 3 – n-hexadecane (approximately 27 mN/m)
- Grade 4 – n-tetradecane (approximately 26 mN/m)
- Grade 5 – n-dodecane (approximately 25 mN/m)
- Grade 6 – n-decane (approximately 24 mN/m)
- Grade 7 – n-octane (approximately 21 mN/m)
- Grade 8 – n-heptane (approximately 20 mN/m)
Contact Angle Measurement
As a supplementary method, an optical sessile drop instrument is used to measure the contact angle of a defined oil droplet, typically n-hexadecane, on the fabric surface. Because capillary wicking within textile structures complicates direct comparison with flat substrates, contact angle data are mainly used for research and development comparisons between finish formulations rather than for pass-fail certification.
Liquid Penetration Resistance for Protective Applications
Where geomagnetic fabric is used in occupational or protective products, penetration resistance against liquid chemicals may additionally be evaluated using the barrier cell method of ASTM F903, which measures whether a test liquid passes through the fabric under specified contact time and pressure.
Durability Testing Sequence
Specimens undergo repeated domestic laundering in accordance with ISO 63300 (formerly ISO 6330) and, where required, abrasion in accordance with the Martindale method of ISO 12947. After the defined treatment cycles, specimens are dried, reconditioned per ISO 139, and re-tested by the hydrocarbon resistance method. The laboratory reports the retained grade and the percentage of initial repellency retained.
Rating and Interpretation
- Grade 0 – fabric wets even with white mineral oil; finish is absent or ineffective
- Grade 3 to 4 – basic protection against heavy oils; suitable for light-duty applications
- Grade 5 – typical acceptance threshold for commercially repellent-finished fabrics
- Grade 6 to 8 – high-performance repellency against low-surface-tension oils; suitable for demanding service conditions
Applications
Oil repellency testing of geomagnetic fabric supports quality control and market access across several product categories:
- Wellness and magnetic therapy apparel, where skin oils and lotions must not stain or degrade the fabric surface
- Magnetic bedding products, underlays, and mattress ticking that require resistance to body oils and household lubricants
- Magnetic insoles, support wraps, and bracing textiles subject to prolonged skin contact
- Healthcare and elderly-care textiles where hygiene and stain resistance are combined with functional comfort
- Manufacturer research and development for benchmarking fluoropolymer versus fluorine-free repellent finishes on magnetic fiber substrates
- Supplier verification, incoming material inspection, and preparation of test reports for buyers, retailers, and regulatory submission in export markets
FAQ
What oil repellency grade should geomagnetic fabric achieve?
For general wellness and bedding applications, a grade 5 result against the ISO 14419 hydrocarbon series is widely regarded as the commercial acceptance threshold. Products marketed with heavy-duty or professional stain-resistance claims should target grade 6 or higher, both initially and after the agreed number of wash cycles.
Do the magnetic particles interfere with the oil repellency test?
No chemically significant interference occurs. The hydrocarbon resistance method evaluates only the outer fabric surface, and magnetic particles enclosed within fiber cores do not react with the test liquids. However, particle-rich surface coatings can raise the effective surface energy of the fabric and reduce the repellency grade, which is exactly the type of quality risk that testing is designed to detect.
How is oil repellency different from water repellency?
Water has a surface tension of about 72 mN/m, whereas common oils and hydrocarbons range from roughly 20 to 30 mN/m. Repelling oils therefore demands a finish with a much lower critical surface energy. A fabric can pass a water spray test yet fail completely against oils, so the two properties must be verified with separate test methods.
How much sample is required and how long does testing take?
A minimum of three full-width pieces of approximately 30 cm x 30 cm per finish variant is recommended, plus additional yardage if durability laundering programs are included. The hydrocarbon resistance test itself is completed within one or two working days after conditioning, while multi-cycle wash durability programs typically extend the turnaround to five to ten working days.