Contents
Partially compliant

AATCC TM 79: test method for absorbency of textiles by drop wetting time

AATCC TM79 times how long a drop of water takes to soak into fabric, the wetting time behind most fabric absorbency claims. With the fabric holder option, the Dropometer uses multi-capture, which takes images over time, to follow the drop from the side with the 10 frames per second camera and times when it sinks in. That is the same end result by a different reading. It does not reproduce the standard's drop delivery or its specular reflection end point, so correlate with TM79 before you report against a TM79 limit.

What brings you here?

Who this is for
Textile mills, finishers, towel, activewear and nonwoven makers, and test labs that check fabric absorbency.
Compliance tier
Partially compliant: the Dropometer times drop absorption on fabric from a side view, the same end result by a different reading. It does not reproduce the standard's drop delivery or its specular reflection end point.
Measurement
Time for a water drop to sink into fabric, filmed at 10 frames per second; water contact angle 10° to 175°, ±0.35° accuracy, on fabrics that do not absorb (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs in the lab or next to the finishing line.
Last updated
October 20, 2026
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Free one page checklist for drop absorbency timing next to AATCC TM79: what to prepare, the settings to lock, how to time each drop and what to record. Made for textile QC and finishing labs.

Talk to an expert

Book a 15 minute demo on your fabric

Tell us your fabric, finish and how you test absorbency today. We will time drops on it live and tell you plainly where the Dropometer fits next to your TM79 stopwatch test and where it does not.

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View the official standard
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
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Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
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Verified against AATCC TM 79
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box

Standard

AATCC TM79-2025, Test Method for Absorbency of Textiles, from AATCC, the American Association of Textile Chemists and Colorists, published in the AATCC Technical Manual. It covers the water absorbency of yarns, fabrics and garments of any fibre and construction, including woven, knit and nonwoven (AATCC store listing).

Compliance tier

Partially compliant. The Dropometer gets the end result the standard is after, the time for a water drop to soak into fabric, by filming the drop from the side. Side view drop timing is an alternative method, not the specular reflection reading the standard specifies. If a contract or customer requires an AATCC TM79 result, run a correlation study on your own samples first.

Instrument performance

Camera 10 frames per second, so times come in 0.1 s steps. Contact angle range 10° to 175°, accuracy ±0.35°, display resolution 0.01°, from the Dropometer product specification. Fabric holder available as an option.

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers. See our validation publications.

Customer evidence

A federal research lab's biomaterials and coatings team uses the Dropometer to measure contact angle on coated fabric. Read the case study. University researchers also used a Droplet Lab goniometer to measure water contact angles of 130.1° to 143.2° on electrospun polystyrene fibre mats (Macromolecular Rapid Communications, 2024). Read our analysis. Neither study ran AATCC TM79.

What it does not tell you

A wetting time shows how fast the fabric surface takes up one drop. It does not measure how far water wicks, how much the fabric holds, or how fast it dries. Those belong to wicking and moisture management tests. Pair it with the test your product claim needs.

Executive summary

What this standard measures, who uses it and how the Dropometer fits

AATCC TM79 (often written AATCC 79, or AATCC Test Method 79) measures how fast a fabric absorbs water: a drop of water lands on taut fabric and you time how long it takes to lose its shine and soak in. Textile mills, finishers, towel and activewear brands and test labs use this wetting time to check scouring, hydrophilic finishes and the effect of washing. The Dropometer is partially compliant. With the fabric holder option it uses multi-capture, which takes images over time, to follow the drop from the side with the 10 frames per second camera and times how long the drop takes to sink into the fabric, the same end result by a different reading. Note that side view drop timing is an alternative method, not the specular reflection reading the standard specifies; if a contract or customer requires an AATCC TM79 result, run a correlation study on your own samples first.

The standard covers yarns, fabrics and garments of any fibre and construction, including woven, knit and nonwoven. Water is delivered from a burette or a dropper held at a set height, and the operator stops the clock when the drop no longer reflects light. Drop size, drop height, conditioning and the time limit are as the standard specifies. For fabrics that do not absorb, such as water repellent finishes, the Dropometer contact angle and surface energy kit reads the water contact angle instead, with ±0.35° accuracy (Dropometer datasheet). The textile DWR water repellency testing use case shows that workflow.

A federal research lab uses the Dropometer to measure contact angle on coated fabric, and university researchers used a Droplet Lab goniometer to measure water contact angles on electrospun polystyrene fibre mats. For background, read the fabrics guide and the contact angle measurement guide.

Further reading: reproducible contact angle measurement, water contact angle reference values for common surfaces, choosing a contact angle goniometer for industrial QA, a classroom experiment on superhydrophobic surfaces on glass and the captive bubble method, which runs with the optional cuvette for samples tested under liquid.

How the Dropometer fits the absorbency test

Timing a water drop on fabric with the Dropometer, step by step, in our own words

From a fabric specimen to a recorded wetting time

These steps describe side view drop timing on the Dropometer. They are not the AATCC TM79 procedure and do not replace it. Buy the current edition and follow it for any result you report to the standard.

10 fps

Camera frame rate

Absorption times in 0.1 s steps. Fine for drops that take about 1 s or longer, not sub second wicking.

±0.35°

Contact angle accuracy

For fabrics that do not absorb. From the Dropometer product specification.

About 2 min

Setup

Base plate, phone holder, LED, syringe and fabric holder. No PC needed.

1

Cut and condition the specimens

Cut specimens from the fabric, yarn or garment, away from edges and creases. Handle them by the corners. Condition them and wash them first if your product claim covers washed fabric, as the standard describes.

2

Mount the fabric flat and taut

Clamp the specimen in the fabric holder so the test area lies flat and taut, the job the embroidery hoop does in the standard. A slack or wrinkled fabric changes how the drop sits and how fast it sinks in.

3

Set up the Dropometer

Level the base plate, mount the phone and LED, and fill the syringe with distilled or deionised water. Focus on the fabric surface so the drop profile and the fabric line are both sharp.

4

Place the drop and start multi-capture

Start multi-capture (images over time, 10 frames per second camera), then form a drop on the needle and bring it down until it touches the fabric. Keep the drop volume the same for every drop. Note that the standard drops water from a burette or dropper at a set height, so this step differs from it.

5

Read the absorption time

Time zero is the first frame where the drop touches the fabric. The end is the first frame where no drop profile remains above the fabric line. If the drop does not soak in within the time limit the standard specifies, read its water contact angle instead.

6

Repeat and record

Place several drops on fresh spots across the specimen. Record the mean and spread, drop volume, room conditions, wash history and the method as side view timing. For good bench habits, see reproducible contact angle measurement.

7

Watch the full measurement

This video shows a complete Dropometer contact angle measurement, from setup to result. It covers the steps above in one run.

Dropometer contact angle measurement, start to finish.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Published contact angle accuracy is ±0.35° (Dropometer product specification).

Read the validation papers

Customer evidence

A federal research lab uses the Dropometer to measure contact angle on coated fabric. We have no published client study run to AATCC TM79 itself.

Read the case study

Set your textile absorbency limit, then correlate

AATCC TM79 · wetting time · textile QC

AATCC TM79 is a test method. Your product specification or your customer sets the pass limit. As one example, Intertek notes that high performance knits are often expected to absorb the drop in 2 seconds or less (source: Intertek HP Mark absorbency page).

Side view timing on the Dropometer is an alternative method, not the specular reflection reading the standard specifies. The two end points can differ, and so can the drop size and the way the drop lands. So run a correlation study before you use Dropometer times against a TM79 limit.

Pick fabrics that span your range, from fast absorbing to slow. Time each fabric by TM79 with a stopwatch and on the Dropometer, on the same day and in the same room. Plot one against the other and set your Dropometer limit from that data. Repeat the study when you change finish chemistry, fibre blend, drop volume or wash protocol.

Example output: drop absorbency on four textiles

Example data for illustration only. These are not measured results. Your own fabrics, finishes and limits decide the numbers.

Example: water drop absorption time on four fabrics, Dropometer side view

Fabric Drops (n) Mean absorption time (s) Std dev (s) Decision (example 2 s limit)
Polyester knit, hydrophilic finish51.30.2Accept
Cotton jersey, after one wash52.60.4Above limit: check scouring and finish
Polyester knit, no finish514.82.3Reject: slow to absorb
Woven, water repellent finish5Did not absorbRead contact angle: example mean 128.4°

How to read this table

Each row is the mean of five drops on one fabric, timed from the frame where the drop touches to the frame where no drop profile remains, in 0.1 s steps. The decision column uses an example limit of 2 s, set from a customer specification and a correlation study.

Example output chart

The same example data as the table, for the three fabrics that absorbed the drop, against the example 2 s limit.

Bar chart of example water drop absorption times of 1.3, 2.6 and 14.8 seconds on three fabrics, against an example 2 second limit

Example data, not measured results.

Business impact

What changes when the drop is filmed, not watched

Metric Before Dropometer With Dropometer Results
How the end point is judged Operator watches the drop lose its shine First frame with no drop profile above the fabric No published benchmark
Time steps Stopwatch started and stopped by hand 0.1 s steps from frames at 10 frames per second Dropometer product specification
Record Time written on a sheet Drop images saved with each time No published benchmark
Fabrics that do not absorb Reported as over the time limit Water contact angle, ±0.35° accuracy Dropometer product specification
Reported TM79 value Burette or dropper and stopwatch Still needs the TM79 procedure, or a correlation study AATCC TM79 scope

See drops timed on your own fabric

Bring a fabric that absorbs well and one that does not. We will time drops on both live.

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ROI estimate

Estimate the cost of the absorbency failures this test can catch

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings

Lock these before you compare absorption times between shifts or sites

Parameter Recommended Setting Technical Rationale
Method Side view drop timing, reported as an alternative method AATCC TM79 times the loss of specular reflection, seen by the operator.
Test liquid Distilled or deionised water, as the standard specifies Dissolved salts or surfactant change the time.
Drop volume Fixed for every drop; record it A bigger drop takes longer to soak in. The Dropometer dispenses from a needle, not a burette.
Specimen mounting Fabric holder, flat and taut, same tension each time Slack fabric changes contact with the drop.
Time zero and end point First touching frame; first frame with no drop profile Fixed frame rules make two operators read the same time from the same video.
Time limit As the standard specifies Drops still on the surface at the limit are read as contact angle instead.
Replicates Several drops on fresh spots per specimen Weave, knit and finish vary across the fabric.
Environment Test in conditioned air; record temperature and humidity The Dropometer has no temperature or humidity control and runs at 10 to 45 °C.

Is AATCC TM 79 the right test, or a moisture management test?

Pick the method by the question you need answered

Start: What do you need to know about how your fabric handles water?

How fast a water drop soaks in

Signals:

You want a time per drop to compare finishes, lots or wash cycles in QC or R&D.

Rule-out:

Use side view drop timing on the Dropometer with the fabric holder. It is partially compliant with AATCC TM79, this page: correlate with TM79 before you compare against a TM79 limit.

A reported AATCC TM79 result

Signals:

Your customer, retailer or performance label programme asks for a wetting time to AATCC TM79.

Rule-out:

Run TM79 as written, with its burette or dropper and the specular reflection end point. Use the Dropometer for that report only after a correlation study on your own fabrics.

Fabric that repels water

Signals:

The drop sits on the surface and does not soak in, as on a DWR finish.

Rule-out:

Read the water contact angle on the Dropometer. For rated repellency, see AATCC TM22 spray testing and AATCC TM193 water and alcohol drops.

How far water wicks or how much the fabric holds

Signals:

Your claim is about wicking distance, water taken up by weight or drying time.

Rule-out:

Use a wicking or absorbency by weight method such as AATCC TM197 or ISO 20158, or a moisture management test such as AATCC TM195. The Dropometer does not measure these.

Decision tree at a glance

Start from the question you need answered. Blue boxes are measurements the Dropometer runs.

Decision tree for choosing between side view drop timing on the Dropometer, AATCC TM79 as written for a reported result, water contact angle for repellent fabric, and a wicking or absorbency by weight method

Is AATCC TM79 the right test?

Interpreting absorbency results

What a wetting time tells you, and what it does not

Shorter time, more absorbent surface: A drop that sinks in fast shows the fibres and finish wet easily and pull water into the fabric.
Washing can shift the time: Finishes wash off and softeners build up. Test before and after the wash cycles your claim covers.
Spread across drops matters: A good mean with a few slow drops points to uneven finish, residual sizing or oil on part of the fabric.
Time is not wicking: A fast wetting time shows the surface takes up a drop. It does not show how far water spreads or how fast the fabric dries.
Expert perspective

Why a single drop reading needs care on fabric

Place a drop and just read it and you get an apparent angle: a value somewhere between advancing and receding that isn't much use. Zisman settled that in the fifties.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Common pitfalls and limits

Honest limits of the method and of the Dropometer

Side view drop timing is an alternative method, not the specular reflection reading AATCC TM79 specifies. Do not swap results without a correlation study on your own fabrics.
The camera runs at 10 frames per second. Time zero and the end point each carry up to 0.1 s, so drops that soak in under about 1 s are at the camera limit.
The Dropometer places the drop from a needle, not from a burette or dropper at a set height. Drop volume and impact both change the time.
Contact angles below 10° are outside the Dropometer range, so time the drop to the frame where its profile is gone rather than to an angle.
The Dropometer has no temperature or humidity control. Test in conditioned air and record the conditions (operating 10 to 45 °C).
Hairy, napped or terry surfaces blur the fabric line in the image. Mark the baseline the same way for every drop.
FAQ

Frequently asked questions

What does AATCC TM79 measure?

It is a method for the determination of the water absorbency of textiles: how fast a fabric takes up a drop of water. A drop of water lands on fabric held taut, and the operator times how long the drop takes to lose its specular reflection and soak in. That time is the wetting time. It applies to yarns, fabrics and garments, woven, knit or nonwoven.

Can the Dropometer run AATCC TM79?

In part, so it is partially compliant. With the fabric holder option it uses multi-capture, which takes images over time, to follow a water drop on taut fabric with the 10 frames per second camera and times how long the drop takes to sink in. That is the same end result by a different reading: side view drop timing is an alternative method, not the specular reflection reading the standard specifies; if a contract or customer requires an AATCC TM79 result, run a correlation study on your own samples first.

Are Dropometer times the same as AATCC TM79 stopwatch times?

Not automatically. TM79 stops the clock when the drop loses its shine, seen from above. The Dropometer stops when no drop profile is left, seen from the side. Drop size and the way the drop lands can also differ. Time the same fabrics both ways and set your limit from that correlation.

What is a good wetting time for fabric?

TM79 is a test method, so your product specification sets the limit. As one example, Intertek notes that high performance knits are often expected to absorb the drop in 2 seconds or less (source: Intertek HP Mark absorbency page). Set your own limit from fabrics that passed and failed in use.

Is the 10 frames per second camera fast enough?

For most fabrics, yes. Frames come every 0.1 s, so a drop that takes a few seconds to soak in is timed in fine steps. Very absorbent towels and knits that take up a drop in under about 1 s are at the camera limit. Use TM79 as written for those.

What if the drop never soaks in?

Then the fabric repels water and the wetting time only tells you it is over the limit. Read the water contact angle on the Dropometer instead, and use AATCC TM22 or AATCC TM193 for rated repellency.

Does the Dropometer control temperature or humidity?

No. The Dropometer has no temperature or humidity control and runs at 10 to 45 °C. Condition the specimens as the standard describes, test in conditioned air and record the room conditions with each result.

Legal note

This page summarises AATCC TM79 in our own words and does not reproduce the standard. Buy the current edition from AATCC before you write a procedure. The Dropometer is partially compliant: it times drop absorption on fabric from a side view, an alternative to the specular reflection reading the standard specifies. Droplet Lab does not certify compliance. Your own method validation does.

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How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

AATCC TM79-2025 listing (AATCC store); AATCC TM79-2025 listing, member store page; Intertek HP Mark: absorbency (AATCC TM79 wetting time, 2 s note for high performance knits); AATCC test methods summary: AATCC 79 absorbency of textiles, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the standard. Buy the current edition for the full procedure.

04

Last checked

October 2026

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References

1. AATCC TM79-2025. members.aatcc.org/store/tm79
2. AATCC TM79-2025 listing, member store page. members.aatcc.org/store/tm79/499/
3. Intertek HP Mark: absorbency (AATCC TM79 wetting time, 2 s note for high performance knits). intertek.com/products-retail/hp-mark/textiles-and-apparel/absorbency/
4. AATCC test methods summary: AATCC 79 absorbency of textiles. aatcctestmethods.com/test-methods/aatcc-79-absorbency-of-textiles/
5. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
6. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/