Contents
Partially compliant

TAPPI T 558: surface wettability and absorbency of paper and board by contact angle

TAPPI T 558 tracks how a drop wets and soaks into paper, board or film over time. The Dropometer reads the water contact angle at the 1.0 s and 10 s check points with ±0.35° accuracy (Dropometer product specification), on a drop shape method validated in two peer reviewed papers. The 0.1 s check point and drop volume tracking need a high speed automated tester.

What brings you here?

Who this is for
Paper mills, converters, printers and makers of absorbent, packaging and paper based diagnostic products.
Compliance tier
Partially compliant: the Dropometer reads the water contact angle at the 1.0 s and 10 s check points, not the 0.1 s check point or drop volume.
Measurement
Water contact angle on paper at fixed times, 10° to 175° range, ±0.35° accuracy, 10 frames per second (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs at the machine or in the lab.
Last updated
October 20, 2026
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Free one page checklist for TAPPI T 558: what to prepare, the settings to lock, which check points the Dropometer covers and what to record. Made for paper and board QC benches.

Talk to an expert

Book a 15 minute demo on your paper or board

Tell us your grade, sizing or coating and your current check. We will show the measurement live and tell you plainly which T 558 check points the Dropometer covers and which it does not.

Book a 15 minute demo
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.
Read More
Verified against TAPPI T 558
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

TAPPI T 558 om-25, Surface wettability and absorbency of sheeted materials using an automated contact angle tester, an Official Method of TAPPI, the Technical Association of the Pulp and Paper Industry. It revises om-20. The method began as a provisional method in 1995.

Compliance tier

Partially compliant. The Dropometer reads the water contact angle at the 1.0 s and 10 s check points. The method also calls for a camera at 50 or 60 images per second, a drop applicator timed to the camera within ±1 ms and drop volume results, which the Dropometer does not provide.

Instrument performance

Contact angle range 10° to 175°, accuracy ±0.35°, display resolution 0.01°, camera 10 frames per second, 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 paper absorbency to this method yet. For a related workflow, see paper microfluidic wicking control.

What it does not tell you

A contact angle over time shows how a surface wets and takes up liquid. It does not replace your print, glue or Cobb test. Pair it with the test your customer specifies.

Executive summary

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

TAPPI T 558 measures how a liquid wets and soaks into paper, board or film by tracking the contact angle and drop volume over time, with the first check point at 0.1 s. Paper mills, converters, printers and makers of absorbent and paper based diagnostic products use it to compare sizing, coatings and surface treatment. The Dropometer is partially compliant: it reads the water contact angle on paper at the 1.0 s and 10 s check points with ±0.35° accuracy, but it does not match the method's 50 images per second camera or its camera timed drop applicator.

The method applies a 4.0 µL drop of reagent water automatically, starts a timer at contact and films the drop as it spreads and absorbs. It reports the average contact angle and drop volume over ten drops at set check points, usually 0.1, 1.0 and 10 s. For the terms used, see the wettability glossary entry.

The Dropometer contact angle and surface energy kit runs on battery, so you can check sized paper and board at the machine or in the lab. For paper diagnostics, see paper microfluidic and lateral flow wicking control. For background, read the packaging and containers guide and the contact angle measurement guide.

Further reading: reproducible contact angle measurement, water contact angle reference values for common surfaces and choosing a contact angle goniometer for industrial QA.

How the Dropometer fits the automated contact angle tester method

The TAPPI T 558 measurement, step by step, in our own words

From paper strip to angles at each check point

These steps outline the procedure and show where the Dropometer differs from the method's apparatus. They do not replace the standard. Buy the current edition and follow its drop size, check points and specimen rules.

±0.35°

Contact angle accuracy

From the Dropometer product specification. Display resolution is 0.01°.

10 fps

Camera frame rate

Fine for check points at 1.0 s and later. T 558 calls for 50 or 60 images per second.

About 2 min

Setup

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

1

Cut and condition the strips

Sample the paper and cut strips to the width the standard specifies. Mark machine direction and which side you test. Condition the strips in a standard paper testing atmosphere, as the standard describes.

2

Set up the Dropometer

Level the base plate, mount the phone and LED, and fill the syringe with reagent water. Set the automatic dropper to 4.0 µL. Lay the strip flat on the stage with the test side up. Custom holders are available on request.

3

Place the drop and mark time zero

Start capture before the drop touches the paper, then place it gently. Take the first frame that shows contact as time zero. At 10 frames per second, time zero is known to within 0.1 s, not the ±2 ms the method sets.

4

Read the angle at each check point

Read the left and right angles at 1.0 s and 10 s after contact. Automatic edge and baseline detection gives the same reading from the same image. Report any reading near 0.1 s as indicative only.

5

Repeat to ten drops

Place each new drop on a fresh area of the strip, at the spacing the standard specifies. Ten drops per specimen give the mean and the coefficient of variation the method reports.

6

Record and report the deviations

Record the mean angle and coefficient of variation at each check point, the liquid, drop size, drop spacing and room conditions. State that the 0.1 s check point and drop volume were not measured to T 558. See reproducible contact angle measurement for good bench practice.

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°.

Read the validation papers

Customer evidence

We have no published client paper or case study on paper absorbency to TAPPI T 558 yet. The paper microfluidics use case shows how fixed time water contact angle readings check barriers and channels on paper.

Read the use case

Set limits for your own paper products

TAPPI T 558 · sizing and absorbency · paper and board QC

T 558 publishes no pass or fail angle. Its precision statement gives a contact angle repeatability of 6% and reproducibility of 13%, and a drop volume repeatability of 10% and reproducibility of 20%, from a 1995 interlaboratory trial on six paper grades with 4 µL drops (source: TAPPI T 558 review draft, 2025).

The standard notes that, when a water based ink is the test liquid, angles of about 90 to 110° tend to print best. Lower angles may feather and higher angles may break the ink line (same source). Treat that as a guide, not a limit.

Set your own accept limit from a correlation study. Measure paper that printed, glued or wicked well and paper that failed, at the same check point, then compare with your print trial or a Cobb test to TAPPI T 441. Repeat the study when you change furnish, sizing, coating or test liquid.

Example output

Example data for illustration only. These are not measured results. Your own paper, test liquid and limits decide the numbers.

Example: four paper and board grades, reagent water, 1.0 s and 10 s check points

Sample Drops (n) Angle at 1.0 s (°) Angle at 10 s (°) CV at 10 s (%) Decision
Sized writing paper10104.2100.33.1Accept
Coated board1086.582.14.0Below limit: run a print trial
Lightly sized copy paper1072.438.67.5Absorbing fast: hold the lot
Tissue10AbsorbedAbsorbedn/aDrop gone before 1.0 s: use a high speed tester

How to read this table

Each row is the mean of ten 4 µL drops. The decision column uses an example accept limit of 90° or higher at 10 s, set from a print trial. The 0.1 s check point is not shown, because the Dropometer does not meet the method's timing there.

Example output chart

The same example data as the table, plotted from 1 s to 10 s. The tissue grade is left out because the drop absorbed before the first reading.

Line chart of example water contact angles from 1 to 10 seconds on sized writing paper, coated board and lightly sized copy paper, with the copy paper angle falling fastest

Example data, not measured results.

Business impact

What changes when you can read the later check points at the machine

Metric Before Dropometer With Dropometer Results
Where the check runs Shared automated tester in a central lab At the machine or converting line, on battery for up to 8 h Dropometer product specification
Result format Sizing judged from a drop test by eye An angle at 1.0 s and 10 s, 0.01° display, ±0.35° accuracy Dropometer product specification
Record Operator note Drop images and angles saved per measurement No published benchmark
Early absorption (0.1 s) Automated tester at 50 images per second Still needs the automated tester TAPPI T 558 apparatus section

See the measurement on your own paper

Bring two samples: one that printed or wicked well and one that did not. We will measure both live at the 1.0 s and 10 s check points.

Book a 15 minute demo Request a quote
ROI estimate

Estimate the cost of the sizing and print 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.

Test method settings

Lock these before you compare results between shifts or sites

Parameter Recommended Setting Technical Rationale
Test liquid Reagent water (ASTM D1193), unless agreed otherwise The method names reagent water. Another liquid of interest that suits the equipment can be used if it is agreed and reported.
Drop volume 4.0 µL, fixed for every drop The standard drop size. The automatic dropper doses down to 0.05 µL.
Drop delivery Needle, automatic dropper; report as a deviation The method uses a pump and a short applicator stroke timed to the camera. The Dropometer has no timed applicator.
Frame rate 10 frames per second The method calls for 50 or 60 images per second, with at least 50 in the first second.
Check points 1.0 s and 10 s; 0.1 s indicative only Frames are 0.1 s apart and time zero is set from the first contact frame.
Fit model Young-Laplace or polynomial, the same for every run Both models are in the Dropometer software. A polynomial fit suits drops that lose symmetry as they absorb.
Replicates Ten drops per specimen, fresh area each time The method reports the mean and coefficient of variation over ten drops.
Environment Test in the conditioning room; record temperature and humidity Paper takes up moisture. The Dropometer runs at 10 to 45 °C and has no humidity control.

Is TAPPI T 558 the right test?

Pick the method by the question you need answered

Start: What do you need to know about how your paper takes up liquid?

Sizing as an angle at 1 s and later

Signals:

You want a measured value per reel for sized paper or board, read at the 1.0 s and 10 s check points.

Rule-out:

Use TAPPI T 558, this page. The Dropometer is partially compliant and covers these check points.

Absorption in the first tenth of a second

Signals:

You test tissue or very absorbent grades, or you need the 0.1 s check point and drop volume over time.

Rule-out:

Use TAPPI T 558 on an automated tester with a camera at 50 images per second or faster.

Water taken up in grams per square metre

Signals:

Your customer specifies water absorptiveness over a set time, not a contact angle.

Rule-out:

Use the Cobb test to TAPPI T 441 or ISO 535. Contact angle complements that check.

One water contact angle by an optical method

Signals:

You need a single angle reading on paper or board, not a curve over time.

Rule-out:

Use ISO/TS 14778 or TAPPI T 458 / ASTM D724.

Decision tree at a glance

Start from the question you need answered. The blue box is the part of this work the Dropometer runs.

Decision tree for choosing between the later TAPPI T 558 check points on the Dropometer, TAPPI T 558 on a high speed tester, the Cobb test and a single water contact angle reading

Is TAPPI T 558 the right test?

Interpreting wettability and absorbency results

What the angle over time tells you, and what it does not

A falling angle means uptake or spreading: If the angle drops fast between 1 s and 10 s, the paper is absorbing or the drop is spreading. A steady angle points to good sizing.
Angle and volume tell different stories: The method tracks drop volume to separate absorption and evaporation from spreading. The Dropometer reads the angle only, so pair it with a Cobb test.
Direction and side matter: Wetting can differ between machine and cross direction, and between the two sides. Test both when they might differ.
Ink is not water: The standard links 90 to 110° with good printing for water based inks as the test liquid. Water readings need their own limits.
Expert perspective

Why the angle over time tracks sizing and absorbency

Pick the measurement to match the question: the same surface can read one way as a sessile drop and another on a tilted plate, and both can be the right answer.

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 camera runs at 10 frames per second. That suits check points at 1.0 s and later, not the 0.1 s check point or millisecond absorption.
The Dropometer has no drop applicator timed to the camera, so time zero carries up to 0.1 s of uncertainty.
Tissue and other very absorbent grades can take up a 4 µL drop before the first useful frame.
The Dropometer has no temperature or humidity control. Test in the conditioning room and record the conditions.
Curled or cockled strips tilt the baseline. Flatten them on a carrier, as the standard describes, before you place the drop.
FAQ

Frequently asked questions

What does TAPPI T 558 measure?

The test method measures the contact angle of a test liquid in contact with paper, paperboard or film over time, and how much of the drop stays on the surface. An automated tester applies the drop and films it. Results are the average angle and volume at set check points, usually 0.1, 1.0 and 10 s.

Can the Dropometer run TAPPI T 558?

In part. The Dropometer reads the water contact angle at the 1.0 s and 10 s check points with ±0.35° accuracy. Its camera runs at 10 frames per second, and it has no drop applicator timed to the camera, so the 0.1 s check point and drop volume results need a high speed automated tester.

What frame rate and earliest reading does TAPPI T 558 call for?

The apparatus section calls for 50 or 60 images per second, with at least 50 images in the first second, and a timer started within ±2 ms of contact. The earliest standard check point is 0.1 s (source: TAPPI T 558 apparatus and report sections).

How is TAPPI T 558 different from TAPPI T 458?

T 458 reads the water contact angle on paper at set times by a goniometer method. T 558 automates the drop and follows the angle and drop volume over time to show absorbency. See TAPPI T 458 / ASTM D724.

Is a contact angle test the same as a Cobb test?

No. The Cobb test weighs how much water a sheet takes up over a set time, in grams per square metre. A contact angle shows how the surface wets. Many mills run both. See TAPPI T 441.

What water contact angle on paper is good?

T 558 publishes no pass or fail value for water. It notes that angles of about 90 to 110° tend to print best when a water based ink is the test liquid. Set your water limit from paper that printed or glued well, at the same check point.

Legal note

This page summarises TAPPI T 558 in our own words and does not reproduce the standard. Buy the current edition from TAPPI before you write a procedure. The Dropometer is partially compliant with this method. 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

TAPPI T 558 listing (TAPPI store); ANSI/TAPPI T 558 om-25 listing; TAPPI T 558 five year review draft, ballot 2 (May 2025); TAPPI standards numerical index (November 2025), 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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Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

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References

1. TAPPI T 558 om-25. imisrise.tappi.org/TAPPI/Products/01/T/0104T558.aspx
2. ANSI/TAPPI T 558 om-25 listing. webstore.ansi.org/standards/tappi/ansitappi558om25
3. TAPPI T 558 five year review draft, ballot 2 (May 2025). tappi.org/contentassets/58af997fbe9b4f40a7545ee183554082/2025/t558-b-2
4. TAPPI standards numerical index (November 2025). tappi.org/contentassets/6d1c3fe50b9643fc9404b2f42e7b12a3/standards_num
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/