Standard Metric
Standardized testing protocols measure the resistance of textile fabrics to wetting by hydrocarbon liquids. Mill quality control laboratories apply AATCC 118 oil repellency to assign a numerical rating from 0 to 8 based on liquid surface tension thresholds. The evaluation determines whether fluorocarbon or fluorine-free finishes maintain chemical barriers against liquid soils.
Testing stops at the surface interaction stage without assessing hydrostatic pressure resistance.
Hydrocarbon Rating
Specified hydrocarbon liquids ranging from mineral oil down to heptane drop onto flat fabric specimens in controlled laboratory environments. Higher numerical scores reflect resistance to liquids with progressively lower surface tension values. Standard oil number 1 uses refined mineral oil at 31.5 dynes per centimetre, whereas oil number 8 uses n-heptane at 20.0 dynes per centimetre.
Droplets remain on the fabric surface for thirty minutes under standard observation criteria.
Liquid Penetration
Wetting occurs when liquid surface energy drops below the critical surface tension of the treated textile substrate. Specimen preparation requires smooth conditioning at standardized temperature and relative humidity levels prior to liquid application. Passing a specific rating indicates that the liquid droplet maintains a clear convex profile without visible surface wicking or substrate darkening.
Failure manifests as liquid absorption, shadow formation, or contact angle breakdown within the thirty-minute exposure window. Commercial buyers specify minimum acceptable ratings based on garment end use, requiring grade 4 for general outerwear and grade 6 for protective workwear.
Chemical Boundary
Repellency performance depends entirely on the low surface energy achieved by surface finishes. Fluorinated chemistries readily achieve ratings of 6 or higher due to perfluoroalkyl groups. Novel fluorine-free formulations generally struggle to pass rating 3 because alkyl and silicone structures lack sufficient resistance against low-tension hydrocarbon fluids.
The test method evaluates surface chemical energy without measuring physical abrasion resistance, laundering durability, or vapor permeability.
