Contents
Partially compliant

ISO 1409: determination of surface tension of polymer dispersions and rubber latices

ISO 1409 measures the surface tension of diluted polymer dispersions and rubber latex with a Du Noüy ring (Method A) or a Wilhelmy plate (Method B) at 23 ± 1 °C. The Dropometer is partially compliant: it measures the same property by pendant drop, with ±0.03 mN/m accuracy (Dropometer datasheet). Pendant drop is an alternative method, not the ring or plate method the standard specifies, and the Dropometer has no temperature control. If a contract or customer requires an ISO 1409 result, run a correlation study on your own samples first.

What brings you here?

Who this is for
Latex and dispersion producers, compounders, and makers of dipped goods, adhesives, coatings and carpet backing.
Compliance tier
Partially compliant: the Dropometer measures latex surface tension by pendant drop, an alternative method to the ring or plate ISO 1409 specifies. No temperature control.
Measurement
Pendant drop surface tension up to 75 mN/m, ±0.03 mN/m accuracy, static and dynamic (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs at the line or in the lab. No temperature control.
Last updated
October 20, 2026
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Free one page checklist for latex surface tension by pendant drop beside ISO 1409: how to prepare the latex, the settings to lock, what to record and how to correlate with your ring results. Made for latex and dispersion QC benches.

Talk to an expert

Book a 15 minute demo on your latex

Tell us your latex or dispersion, its solids content and your current ring check. We will show a pendant drop reading live and tell you plainly where it fits beside ISO 1409 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
Read More
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.
Read More
Verified against ISO 1409
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

ISO 1409:2020, Plastics/rubber, Polymer dispersions and rubber latices (natural and synthetic), Determination of surface tension. Sixth edition of this international standard from ISO/TC 45/SC 3, the International Organization for Standardization committee for rubber raw materials including latex, confirmed at the 2025 systematic review. It replaces ISO 1409:2006 and adds the plate method. In Germany, DIN ISO 1409:2008-11 adopted the 2006 edition, titled determination of surface tension by the ring method; DIN lists it as withdrawn.

Compliance tier

Partially compliant. ISO 1409 specifies a Du Noüy ring or a Wilhelmy plate, with a bath held at 23 ± 1 °C. The Dropometer measures the same property, the surface tension of the diluted latex, by pendant drop. Pendant drop is an alternative method, not the ring or plate method the standard specifies, and the Dropometer has no temperature control. If a contract or customer requires an ISO 1409 result, run a correlation study on your own samples first.

Instrument performance

Pendant drop surface tension up to 75 mN/m, accuracy ±0.03 mN/m, resolution 0.01 mN/m, static and dynamic, from the Dropometer product specification.

Peer reviewed method

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

Customer evidence

We have no published client paper or case study on latex surface tension yet. For good bench practice, see reproducible surface tension measurement.

What it does not tell you

Surface tension shows how much surfactant sits at the surface. It does not measure stability, viscosity or film formation, so pair it with your other latex tests.

Executive summary

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

ISO 1409 measures the surface tension of polymer dispersions and natural or synthetic rubber latex, diluted to 40% total solids, with a Du Noüy ring (Method A) or a Wilhelmy plate (Method B). Latex producers, compounders and makers of dipped goods, adhesives, coatings and carpet backing use it to check surfactant level and wetting from lot to lot. The Dropometer is partially compliant: it gets the result the standard is after, latex surface tension, by pendant drop with ±0.03 mN/m accuracy (Dropometer datasheet). Pendant drop is an alternative method, not the ring or plate method the standard specifies, and the Dropometer has no temperature control for the 23 ± 1 °C test. If a contract or customer requires an ISO 1409 result, run a correlation study on your own samples first.

The 2020 edition is the sixth. It added the plate method and states that the ring method is preferred in a dispute. Method A is valid for polymer dispersions and rubber latices with a viscosity less than 200 mPa·s, and Method B is not for latex with cationic surfactants. For the method behind the numbers, see the surface tension measurement guide and our notes on reproducible surface tension measurement.

The Dropometer pendant drop tensiometer runs on battery and needs only a syringe of latex, so you can screen lots at the reactor or compounding area between ring tests. Keep a ring or plate tensiometer for results you report to ISO 1409 until your correlation study supports pendant drop. Check it first with water against surface tension reference values for common liquids. If you are choosing an instrument for routine checks, read the best tensiometer for production QC.

ISO 1409 measures surface tension against air. With the optional cuvette, the Dropometer also measures interfacial tension by pendant drop of one liquid in another, which suits oil and water work such as insulating oil ageing checks.

Further reading: the plastics guide and a lubricant base oil maker using a modular Dropometer.

How the Dropometer fits beside surface tension by the ring method

The ISO 1409 sample preparation, with a pendant drop reading, step by step in our own words

From latex sample to a recorded surface tension

These steps outline the sample preparation in ISO 1409 and a pendant drop reading of the same property. They do not replace the standard document. Pendant drop is an alternative method, so label the reading as pendant drop. Buy the current edition and follow its dilution, temperature and calibration rules.

±0.03 mN/m

Surface tension accuracy

From the Dropometer product specification. Resolution is 0.01 mN/m, range up to 75 mN/m.

About 2 min

Setup

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

23 °C

ISO 1409 test temperature

Held to ±1 °C in a bath. The Dropometer has no temperature control, so condition the latex and record the room.

1

Check solids and dilute

Find the total solids of the lot, then dilute with carbon dioxide free grade 3 water to 40% total solids, as the standard specifies. Dilute further if viscosity could exceed 200 mPa·s. Find the density of the diluted latex too, as the standard describes, because pendant drop needs it.

2

Bring the latex to temperature

ISO 1409 tests at 23 °C ± 1 °C, or 27 °C ± 1 °C in tropical countries. The Dropometer has no temperature control. Condition the latex and the water in a room or bath at the test temperature, and record the room temperature at the bench.

3

Set up and check with water

Level the base plate, mount the phone and LED, and fill a clean syringe with the same grade 3 water. Read a pendant drop of water and compare it with a value from surface tension of common liquids at your room temperature.

4

Form the latex drop

Fill a clean syringe with freshly stirred latex, free of air bubbles. Enter the latex density. Form a pendant drop large enough to show a clear neck, and keep the size similar for every drop.

5

Read at a fixed drop age

Latex can form a skin, and surfactant keeps moving to a new surface, so read every drop at the same drop age. The Young-Laplace fit gives the surface tension from the drop profile. Use a fresh drop for each reading and flush the needle with water between lots.

6

Record and label the result

Record the mean and spread, solids content, density, drop age and room temperature. Label the result as pendant drop, an alternative method to the ISO 1409 ring, and compare it with limits from your own correlation study against the ring method.

7

Watch the full measurement

This video shows a complete Dropometer pendant drop surface tension measurement, from setup to result. It covers the steps above in one run.

Dropometer pendant drop surface tension, 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 surface tension accuracy is ±0.03 mN/m.

Read the validation papers

Customer evidence

We have no published client paper or case study on latex surface tension yet. Our bench practice notes show how to get repeatable pendant drop readings on surfactant solutions.

Read the bench practice notes

Check against water, then set limits from your own latex

ISO 1409 · latex surface tension · dispersion QC

ISO 1409 calibrates the ring or plate tensiometer against a standard mass or a reference liquid such as water or toluene. For the Dropometer, check the setup with a pendant drop of the same grade 3 water and compare it with a published value at your room temperature (see surface tension of common liquids).

The standard gives a temperature coefficient for latex of about 0.1 mN/m lower per °C rise, between 20 and 30 °C (source: ISO 1409:2020, apparatus clause). So a room 2 °C off the 23 °C test temperature shifts a reading by about 0.2 mN/m. Record the room temperature with every result.

ISO 1409 publishes no pass or fail value. Pendant drop and ring readings are not interchangeable without a correlation study. Measure the same diluted lots by Method A and by pendant drop, at the same temperature and drop age, then set your accept limits from that data. Repeat the study when you change polymer, surfactant package or solids content.

Example output: natural and synthetic latex lots

Example data for illustration only. These are not measured results. Your own latex, dilution, drop age and limits decide the numbers.

Example: water check and three latex lots, diluted to 40% total solids, pendant drop at 30 s drop age

Sample Total solids (%) Drops (n) Mean surface tension (mN/m) Std dev (mN/m) Decision
Water check (grade 3)n/a572.30.1Matches reference value: run the latex
Natural rubber latex, lot A40.0541.20.3Accept
Carboxylated SBR latex40.0544.60.4Accept
Natural rubber latex, lot B40.0536.10.5Below band: check surfactant dosing, confirm by ring

How to read this table

Each row is the mean of five fresh pendant drops in a room at 23 °C. The decision column uses an example accept band of 38 to 46 mN/m, set from a correlation study against the ring method. The water row checks the setup before the latex runs.

Example output chart

The same example latex data as the table, plotted against an example accept band. The water check is left out of the chart.

Bar chart of example pendant drop surface tension for three latex lots against an example accept band of 38 to 46 mN/m, with one natural rubber lot below the band

Example data, not measured results.

Business impact

What changes when you can read latex surface tension at the line

Metric Before Dropometer With Dropometer Results
Where the check runs Ring tensiometer in a central lab At the reactor or compounding area, on battery for up to 8 h Dropometer product specification
Sample needed About 25 cm³ of diluted latex in a dish A syringe of diluted latex ISO 1409 procedure; no published benchmark for the syringe volume
Result format Maximum ring or plate force, converted to mN/m Surface tension from the drop profile, ±0.03 mN/m accuracy Dropometer product specification
Test temperature Bath held at 23 °C ± 1 °C Room conditioned and recorded; no temperature control ISO 1409 apparatus clause; Dropometer product specification

See a pendant drop reading on your own latex

Bring two lots: one that ran well and one that did not. We will measure both live and compare them with your ring results.

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ROI estimate

Estimate the cost of the latex lot failures this check 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 pendant drop results with ring results

Parameter Recommended Setting Technical Rationale
Method Pendant drop; label the result as pendant drop The standard specifies a Du Noüy ring (Method A) or a Wilhelmy plate (Method B). Pendant drop is an alternative method, so correlate it with the ring on your own latex.
Total solids 40% ± 1%, as the standard specifies The standard dilutes to this level. Record the final solids if you dilute further.
Viscosity Below 200 mPa·s The ring method limit. A viscous drop also takes longer to settle, so wait until it stops moving.
Density Measured on the diluted latex, as the standard describes Pendant drop needs the density. An error here moves the result.
Temperature 23 °C ± 1 °C room; record it The standard sets this test temperature. The Dropometer runs at 10 to 45 °C and has no temperature control.
Drop age Fixed, the same for every drop Surfactant keeps adsorbing and latex can skin, so the reading changes with time.
Fit model Young-Laplace The pendant drop fit in the Dropometer software.
Replicates Several fresh drops per lot Report the mean and spread. Flush the needle with water between lots.

Is ISO 1409 the right test?

Pick the method by the question you need answered

Start: What do you need to know about your latex or dispersion?

Latex surface tension for QC, screening or R&D

Signals:

You want a surface tension number per lot to trend surfactant level.

Rule-out:

Use a pendant drop reading on the Dropometer. It measures the same property by an alternative method to the ring or plate. Set limits from a correlation study against the ring method.

A result reported to ISO 1409, or a dispute

Signals:

Your customer or specification names ISO 1409, or two labs disagree.

Rule-out:

Pendant drop is an alternative method, not the ring or plate method the standard specifies. Use a ring tensiometer to Method A, or a plate tensiometer to Method B, with a bath at 23 °C, or run a correlation study on your own samples first. The standard prefers Method A in a dispute.

Oil against water, not latex against air

Signals:

You need the tension between two liquids, for example insulating oil and water.

Rule-out:

Use the Dropometer with the optional cuvette: it measures interfacial tension by pendant drop of one liquid in another. For insulating oil test methods, see ASTM D971 / IEC 62961.

How fast surfactant reaches the surface

Signals:

You compare surfactant packages and need surface tension over drop age, not one value.

Rule-out:

Use dynamic pendant drop on the Dropometer, read at 0.1 s and later. See the surface tension measurement guide.

Decision tree at a glance

Start from the question you need answered. Blue boxes are the measurements the Dropometer runs: pendant drop surface tension, dynamic pendant drop, and interfacial tension with the optional cuvette. A result reported to ISO 1409 needs a ring or plate tensiometer, or a correlation study first.

Decision tree for latex surface tension: Dropometer pendant drop for QC and R&D, ring or plate or a correlation study for an ISO 1409 result, interfacial tension with the optional cuvette, and dynamic pendant drop

Is ISO 1409 the right test?

Interpreting latex surface tension results

What latex surface tension tells you, and what it does not

Lower value, more surfactant at the surface: A lot that reads well below the band often carries extra surfactant, or a different package. A high reading can mean too little.
Drop age changes the reading: Surface tension falls as surfactant adsorbs on a fresh surface. Compare only readings taken at the same drop age.
Temperature moves the number: ISO 1409 gives about 0.1 mN/m lower per °C rise from 20 to 30 °C. Record the room so you can compare lots fairly.
Pendant drop is an alternative method: Pendant drop and ring can read differently on the same latex. Run a correlation study on your own samples before you compare them or report an ISO 1409 result.
Expert perspective

Why latex surface tension depends on drop age and temperature

Surface tension versus concentration is one of the few measurements that lets you watch a surfactant reorganise an interface in real time: read the curve, not just the endpoint.

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

The Dropometer has no temperature control. Condition the latex at the test temperature and record the room.
Latex dries and skins in air. Use a fresh drop for each reading and read at a fixed drop age.
Latex can coagulate in the needle. Flush with water between lots and replace a partly blocked needle.
A wrong density input biases the result. Measure the density of the diluted latex, not the concentrate.
The camera runs at 10 frames per second. That suits readings at 0.1 s and later, not millisecond adsorption studies.
Pendant drop results are not interchangeable with ring results without a correlation study on your own latex.
FAQ

Frequently asked questions

What does ISO 1409 measure?

It measures the surface tension of polymer dispersions and natural or synthetic rubber latex against air. The latex is diluted to 40% total solids, held at 23 °C, and measured with a Du Noüy ring (Method A) or a Wilhelmy plate (Method B).

Which edition of ISO 1409 is current?

ISO 1409:2020, the sixth edition. ISO confirmed it at the 2025 systematic review. It replaced ISO 1409:2006, which covered the ring method only, and added the plate method with its own precision data.

Is the Dropometer compliant with ISO 1409?

Partially compliant. The Dropometer gets the result ISO 1409 is after, latex surface tension, with ±0.03 mN/m accuracy (Dropometer datasheet). Pendant drop is an alternative method, not the ring or plate method the standard specifies, and the Dropometer has no temperature control. If a contract or customer requires an ISO 1409 result, run a correlation study on your own samples first.

Ring or plate: which ISO 1409 method should I use?

The ring method (Method A) is preferred in a dispute and applies below 200 mPa·s. The plate method (Method B) is not for latex with cationic surfactants. Follow the method your customer or specification names.

Do pendant drop and ring results agree?

Not automatically. The methods measure the surface in different ways, and surfactant adsorption over time affects each one differently. Measure the same lots by both methods at the same temperature, then set your limits from that correlation study.

Does the Dropometer measure interfacial tension?

Yes, with the optional cuvette: it forms a pendant drop of one liquid inside another, such as water in insulating oil. ISO 1409 itself covers surface tension against air. For oil and water test methods, see ASTM D971 / IEC 62961.

What is DIN ISO 1409, and is it still current?

DIN ISO 1409:2008-11 was the German adoption of ISO 1409:2006, for the determination of the surface tension of polymer dispersions and rubber latices by the ring method. DIN lists it as withdrawn. The current international edition is ISO 1409:2020, which adds the plate method. If a specification still cites DIN ISO 1409, agree with your customer which edition applies.

Legal note

This page summarises ISO 1409 in our own words and does not reproduce the standard. Buy the current edition from ISO or your national standards body before you write a procedure. The Dropometer is partially compliant: pendant drop is an alternative method, not the ring or plate method the standard specifies. If a contract or customer requires an ISO 1409 result, run a correlation study on your own samples first. Droplet Lab does not certify compliance. Your own method validation does.

View the official standard Book a 15 minute demo

How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

ISO 1409:2020 listing (ISO); ISO 1409:2020 listing (Austrian Standards); ISO 1409:2020 preview pages (iTeh): foreword, scope, principle, apparatus, sample preparation; ASTM D1417-16(2026) listing, 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. ISO 1409:2020. iso.org/standard/75823.html
2. ISO 1409:2020 listing (Austrian Standards). austrian-standards.at/en/shop/iso-1409-2020-2020-08-21~p2545973
3. ISO 1409:2020 preview pages (iTeh): foreword, scope, principle, apparatus, sample preparation. iteh.es/catalog/standards/iso/58e3aa2d-f853-4e27-ab4c-c96aa5ee5bd8/iso
4. ASTM D1417-16(2026) listing. store.astm.org/d1417-16r26.html
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/