Fabrics Guide: Water Repellency and Contact Angle Testing

Executive summary

What it covers: How textile teams use contact angle, sliding angle and surface tension to screen water and oil repellent finishes and printing on fabric. Each measurement is tied to a textile problem, an AATCC method and published client work.
Key insights: The AATCC TM22 spray test gives the final water repellency grade, and contact angle data can anticipate and explain it. A Cornell fiber study found that adding lignin raised the water contact angle of PLA fiber mats in nearly every case. Drops can sink into fabric, so always report when the angle was read.
Business value: Contact angle screening lets you sort finish lots before a full spray test run and find the likely cause of a poor grade. One portable kit covers contact angle, sliding angle and the surface tension of your test liquids.
Standards to follow: AATCC TM22 is a spray test with a visual grade, and contact angle complements it rather than replacing it. AATCC TM118 and TM193 grade oil and aqueous liquid repellency with test liquids, and AATCC TM 79 times how fast fabric absorbs a water drop.
Bottom line: Calibrate contact angle against your own TM22 grades for each fabric family, then use it to screen lots and finishes. Book a 15-minute consult about testing it on your own swatches.

Where wetting decides yield

In textiles, many returns and rework start at the fabric surface. A water repellent finish that wets out in the rain fails the wearer, even when the fabric passed its strength tests. An ink that spreads too far into the yarn blurs a printed design.

Use case

Textile DWR Water Repellency Testing

Contact angle with roll off angle compares DWR finishes and lots, including fluorine free ones, as a complement to the TM22 spray grade rather than a replacement.

Read the use case

Use case

PFAS-Free Reformulation & Repellency

Water and oil contact angles, fresh and after washing or abrasion, show whether a PFAS free finish still repels oil as well as water once fluorinated chemistry comes out.

Read the use case

The Dropometer contact angle and sliding angle kit measures contact angle, surface and interfacial tension, surface free energy and sliding angle with one portable setup. Its method was validated against a KRUSS DSA100E in two peer reviewed papers. If you are new to the terms, start with wettability.

Which measurement for which problem

A dot means the measurement is the main check for that problem.

Problem	Contact angle	Surface and interfacial tension	Surface energy	Sliding angle
Textile DWR Water Repellency Testing
PFAS-Free Reformulation & Repellency

The four measurements behind this guide

Not sure which test you need? Start with how to choose a wettability testing method.

Sample image taken from Droplet Lab Dropometer.

Contact angle

The angle a liquid drop makes where it meets a solid, in degrees. A low angle means the liquid spreads; a high angle means it beads. Use static angles for quick checks, and advancing and receding angles on real, rough or patchy surfaces, where one static value can mislead.

Watch the contact angle demo Read the full contact angle guide

Surface and interfacial tension

The force at a liquid surface that pulls it to the smallest area, in mN/m. The Dropometer measures it from the shape of a hanging (pendant) drop, and interfacial tension from a drop of one liquid inside another. Use static values for batch checks and dynamic values when interfaces form fast.

Watch the surface and interfacial tension demo Read the full surface and interfacial tension guide

Surface energy

The energy needed to create new solid surface, in mJ/m². It is worked out from contact angles of two or more probe liquids. Use it before bonding, printing or coating to check that a surface is clean and treated enough.

Watch the surface energy demo Read the full surface energy guide

Sliding angle

The tilt, in degrees, at which a drop starts to roll or slide off a surface. Use it for water and oil repellent surfaces, where a high contact angle alone does not show that drops will shed.

Watch the sliding angle demo Read the full sliding angle guide

Glass - DI Water

Nylon - DI Water

PMMA - DI Water

Teflon - DI Water

The droplet images above are taken from the same benchmark series as our open dataset. For each substrate and probe liquid we report:

● Advancing and receding contact angles (and hysteresis)
● Derived surface energy (SFE) values based on multi-liquid measurements
● Measurement conditions, uncertainties, and sample preparation details

Comparing your own droplet shapes and angles against these references is a fast way to spot contamination, treatment drift, or unexpected changes in wettability.

Explore the full benchmark datasets (contact angle + surface energy)

Case studies

Fabrics teams using the Dropometer.

Case study
How Cornell University’s materials research facility added a shared Dropometer, and a fiber lab’s water contact angles showed lignin makes PLA mats more water repellent
Water contact angle on eleven electrospun mats ranged from 110.75 degrees for neat PLA to 138.67 degrees with Alcell lignin, with nine of ten blends above neat PLA.

Read the case study
Case study
How an Iowa State University coatings lab measures wetting on coated fabrics with the Dropometer
The group added a Dropometer with an automatic dropper to measure contact angle and roll off on coated fabrics, using both water and oils.

Read the case study
Case study
How a Canadian federal research lab set up water contact angle measurement for repellent coatings on white polyester fabric, a hard sample to image
A government biomaterials and coatings team used the Dropometer to measure contact angle on water repellent coatings applied to white polyester fabric.

Read the case study
Case study
How a University of Calgary chemical engineering department measured water contact angles up to 143° on electrospun polystyrene fibres
Water contact angle on twelve electrospun polystyrene mats ran from 130.1 to 143.2 degrees, showing how spinning conditions set the repellency of nonwoven fiber mats.

Read the case study

Client citations

Published studies that measured with the Dropometer. Our analysis explains what was measured and how; the original paper is linked beside it.

Influence of Mixed Solvent in the Morphology and Hydrophobicity of Electrospun Polystyrene Porous Fibers
The authors measured water contact angle with the Dropometer across solvent ratios and voltages, finding angles generally rose with voltage and peaked at 143.2 degrees.

Read our analysis Read the original paper
Multifunctional, Flexible, Electrospun Lignin/PLA Micro/Nanofiber Mats from Softwood Kraft, Hardwood Alcell, and Switchgrass CELF Lignin
Measured with the Dropometer, nearly every lignin blend raised water contact angle above neat PLA, a route to bio based hydrophobic mats though none reached 150 degrees.

Read our analysis Read the original paper

Industry standards

Standards that describe these measurements for Fabrics. Our page explains how the Dropometer fits each one; the standard itself is sold by its publisher.

AATCC TM 79
Towels, wipes and wicking fabrics are judged by how fast a water drop sinks in; timed side view images record the falling contact angle until the drop is absorbed.

Learn how the Dropometer applies AATCC TM 79 Read the AATCC TM 79 standard
AATCC TM118
For stain and oil repellent finishes, the contact angle of each hydrocarbon test liquid on the fabric puts a number behind the visual grade the method assigns.

Learn how the Dropometer applies AATCC TM118 Read the AATCC TM118 standard
AATCC TM193
Contact angles of the graded water and isopropanol liquids on a finished fabric, plus a pendant drop check of each liquid, show where the finish starts to wet.

Learn how the Dropometer applies AATCC TM193 Read the AATCC TM193 standard
AATCC TM22: Water Repellency Spray Test
The spray rating stays the final grade for rainwear and outdoor gear; water contact angle and sliding angle help screen finish lots before a full spray run.

Learn how the Dropometer applies AATCC TM22: Water Repellency Spray Test Read the AATCC TM22: Water Repellency Spray Test standard

Frequently asked questions

Which measurement should a textile lab start with?

Start with the grade you need to predict. For water repellent finishes, use water contact angle at a fixed time and sliding angle. For oil repellency, measure the contact angle of each test liquid on the fabric. For printing, measure ink surface tension first. Our contact angle and sliding angle guides explain each method.

Which AATCC methods relate to contact angle?

AATCC TM22 is a spray test with a visual grade. TM118 and TM193 grade oil and aqueous liquid repellency with sets of test liquids, and TM 79 times drop absorption. The Dropometer uses the sessile drop method, which adds numbers to these methods. It does not replace their grades, so correlate readings with your own results.

Can contact angle replace the AATCC TM22 spray test?

No. TM22 gives the final pass or fail grade, and there is no published conversion from contact angle to spray rating. Contact angle helps you screen lots before a full TM22 run and explain a poor grade. Set your own pass bands by testing 10 to 20 swatches per fabric family with both methods, as our TM22 page explains.

Why does the contact angle on fabric change over time?

Fabric is porous and rough, so a drop can slowly sink in or spread along the yarns. The angle you read at 2 seconds can differ from the one at 10 seconds. Read every sample at the same drop age, and report that time with the result. See surface roughness and heterogeneity.

What is a good water contact angle for a repellent fabric?

There is no single number, because weave, fiber and finish all change the reading. Surfaces above 90 degrees are called hydrophobic, and 150 degrees is the usual threshold for superhydrophobic. In the Cornell study of lignin and PLA fiber mats, the best mat read 138.67 degrees, below that threshold. Set your own limits against TM22. See hydrophobic and hydrophilic surfaces.

How do I measure oil repellency with contact angle?

Place a drop of each AATCC TM118 test liquid on the fabric and measure its contact angle at a fixed time. The liquids have falling surface tensions, so the angle drops as the liquid becomes more oily. Check each liquid's surface tension by pendant drop before you start. The visual grade stays the reference. See AATCC TM118.

How accurate is the Dropometer?

The drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Contact angle accuracy is 0.35 degrees in the Dropometer product specification. Automatic edge and baseline detection gives the same reading from the same image. See our validation papers.

See it on samples like yours

Book a 15 minute consult and we will show the Dropometer measuring the kind of surface or liquid your team works with.

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Further resources

Every page and paper referenced in this guide, grouped by type.

Fabrics Industry: The Practical Guide to Surface Science (2026)