Contents
Functional Hydrophobicity, Self-Cleaning and Anti-Soiling

Anti-Fog Coating Validation: Contact Angle Checks for Anti-Fog Lens, Visor and Permanent Anti-Fog Coatings

An anti-fog coating works when condensation spreads into a thin, clear film instead of tiny droplets that scatter light. Measure the water contact angle that behaviour depends on, after washing, abrasion and ageing as well as on day one, and confirm with the standard fog test.

Who this is for: Coating developers and quality teams for eyewear, safety goggles, face shields, visors, automotive glass and lamps, camera lenses, medical devices and anti-fog food packaging.

Where it fits: Formulation screening, cure and coating process checks, durability testing after cleaning and abrasion, and incoming inspection of coated parts.

What it does not do: It does not replace EN 168, ISO 16321-1, ANSI/ISEA Z87.1 or other time to fog tests, and it does not measure light transmission.

Method
Sessile drop water contact angle at a fixed early read time, before and after durability tests
Standard
Supports, and does not replace, fogging tests in eye protection standards; ISO 27448 measures contact angle on photocatalytic surfaces
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Gloved hands holding a glass slide over hot water, fogged on the uncoated half and clear on the coated half
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
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
Why it matters

Why anti-fog coating checks matter

88%

of 253 healthcare workers in a survey reported fogging of goggles, spectacles or face shields among the problems of wearing protective equipment.

Agarwal, Agarwal and Motiani, Cureus 12(11):e11652, 2020

Below 5° to 13.8°

rise in water contact angle on a superhydrophilic anti-fog coating after a 50 day ageing test, while it held near 5° after boiling and abrasion.

Liu et al., RSC Advances 13:23409, 2023

24°

water contact angle of a pullulan coating that kept refrigerated food packaging clear by forming an invisible, continuous thin layer of water, so the right angle depends on the product.

Introzzi et al., ACS Appl. Mater. Interfaces 4(7):3692, 2012

Sources: Agarwal A., Agarwal S., Motiani P., Difficulties encountered while using PPE kits and how to overcome them, Cureus, 2020; Liu X. et al., Double cross linked transparent superhydrophilic coating capable of anti fogging even after abrasion and boiling, RSC Advances, 2023; Introzzi L. et al., Wetting enhancer pullulan coating for antifog packaging applications, ACS Applied Materials and Interfaces, 2012. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this anti-fog coating check does and what it does not

A quick reference for anti-fog coating teams checking fit before reading further.

Evidence Box

Problem this solves

Anti-fog coatings that pass the fog test when new but lose performance after washing, wiping, abrasion or ageing, with no number to track the change.

Standards

Fogging tests sit in EN 168, ISO 16321-1 and ANSI/ISEA Z87.1. None we found sets a contact angle limit; contact angle supports those tests.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

No anti-fog case study yet. A Zeus Industries quality engineer completed a gage R&R study on the Dropometer and reported it performed very well.

Published research

Published anti-fog coatings read below 10° water contact angle, and several drift upward after ageing or wear.

Honest limit

Contact angle is not a fog test. Light transmission and time to fog need their own tests.

Who this is for

What anti-fog question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Coating developer

You formulate hydrophilic coatings for anti-fog lens, visor and face shield products, or anti-fog films for food packaging. Contact angle on each formulation and after durability tests shows which keep their anti-fog properties and which make durable anti-fog coatings.

Read the angle at a fixed early time; hydrophilic coatings absorb or spread the drop fast.

Coating line or quality engineer

You apply anti-fog treatment to eyeglass, safety glasses and goggles, or automotive lamps and windshield parts. A contact angle on each lot catches cure and contamination problems before parts ship, so high-performance anti-fog parts stay consistent.

Set gates from parts that passed your fog test.

Medical or camera optics team

You protect optics in medical devices or camera lenses where fog blocks clear vision. Contact angle after cleaning and sterilising shows whether the coating survives harsh chemicals.

Measure after your real cleaning cycle, not only on new parts.
Fit check

Is this the right check for your anti-fog coating?

It measures how water meets the coated surface. It does not measure fogging directly.

Good fit if

You compare anti-fog formulations, anti-fog technology or coating processes.
You check durability after washing, wiping, abrasion or ageing.
You check lots of anti-fog coated lenses, visors or films and other anti-fog products.
You compare permanent anti-fog coatings with sprays and wipes.
You study photocatalytic or superhydrophilic surfaces.

Less relevant if

You need a certified fog test result.
You need light transmission or haze.
Your anti-fog approach relies on droplets rolling off; add sliding angle.
Your parts are too curved to hold a drop without a flat witness sample.
Summary

How contact angle supports anti-fog coating validation

The answer in under a minute.

Measure water contact angle on each anti-fog coating at a fixed early read time, new and after washing, abrasion and ageing. A low angle that stays low means water will spread into a clear film; a rising angle warns that fog performance is fading. Confirm with the fog test your product standard uses.

The Dropometer contact angle kit runs the measurement. Our article on the science of anti-fog coatings, our contact angle measurement guide and wettability glossary entry explain the physics, and the ISO 27448 page covers contact angle on photocatalytic surfaces. Our automotive guide covers glass and lamps.

Expert Quote

Expert perspective on repellency and mobility

“

Repellency and mobility are not the same thing: a high contact angle says a drop is repelled, but whether it rolls off is a separate question; the two can even be mutually exclusive.

Dr. Alidad Amirfazli

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

The problem

Why anti-fog performance is hard to verify

Fog forms when water vapor in moist air meets a surface below its dew point and condenses as tiny droplets. On an untreated lens or visor those water droplets on surfaces scatter light, cut light transmission and leave foggy lenses, a safety problem for safety goggles, face shields and visors and glasses worn by surgeons and medical staff. In one survey of 253 healthcare workers, 88% reported fogging of goggles, spectacles or face shields. Modern anti-fog coatings are designed to attract water: hydrophilic coatings lower the contact angle so water molecules spread into a thin film that stays clear, which is the science behind anti-fog coatings. Anti fog coatings and other anti-fog solutions, from coated lenses to anti-fogging films, are used across a wide range of applications, from goggles to bathroom mirrors. Published anti-fog coatings read below 10°, some below 5°, which is how they maintain clear vision. The difficulty is durability. A coating that is superhydrophilic on day one can drift: one study saw the angle rise from below 5° to 13.8° after 50 days of ageing, and clean superhydrophilic surfaces can turn noticeably hydrophobic within hours as organic contamination builds up. Sprays and wipes wear off faster than a permanent coating, and cleaning with harsh chemicals or abrasion can strip a coating. Fog tests in eye protection standards give a pass or fail for the finished part, but they are slow, so teams need a quick number to track coating performance through research and development, production and environmental conditions, ensuring clear vision for the user.

Lenses or visors fog after a few washes or wipes.
Fog test results vary between coating lots.
Coated parts pass when new but fail after storage.
Anti-fog films fog over in chilled food packaging.
Customers report glasses fogging during use.
Troubleshooting

Why anti-fog coatings fail and what to check

Why:

  • Clean hydrophilic surfaces pick up organic contamination from air and handling, which raises the angle.

How to detect:

  • The angle rises during storage while the coating is intact.

Corrective action:

  • Control storage and packaging, and measure at a fixed time after cleaning.

Why:

  • Wiping, washing and abrasion thin or remove the coating.

How to detect:

  • The angle rises after durability cycles.

Corrective action:

  • Measure after each block of cycles and compare formulations on the same test.

Why:

  • Under cured coatings dissolve or swell when washed.

How to detect:

  • Angles vary across a lot or change after the first wash.

Corrective action:

  • Check cure time, temperature or UV dose, and measure each lot.

Why:

  • Some hydrophilic additives migrate or lose activity in damp heat.

How to detect:

  • The angle rises after humidity ageing.

Corrective action:

  • Add damp heat ageing to development tests and track the angle over time.

Why:

  • Photocatalytic anti-fog surfaces become superhydrophilic only under UV light.

How to detect:

  • The angle is high indoors and low after UV exposure.

Corrective action:

Measure under defined illumination, as the ISO 27448 page describes.

Why:

On very hydrophilic surfaces the drop spreads within a second, so timing changes the reading. Our guide to reproducible contact angle measurement covers fair comparisons.

How to detect:

A reference sample reads differently between sessions.

Corrective action:

Fix drop volume and read time, and measure a reference sample every session.

Not sure why your anti-fog coating fails after washing?

Send new and worn coated samples, and we will compare them on a call.

Book a 15 minute demo
Lab records

What an anti-fog coating record contains

Each check produces a record you can file with the formulation or lot, beside fog test and light transmission results.

Sample

Product, substrate, coating formulation, lot and coating process.

History

New, after washing or wiping cycles, after abrasion, or after ageing, with counts and conditions.

Method settings

Drop volume, read time, temperature and humidity.

Readings

Contact angle at each spot, the median and spread, and the change from new.

Decision

Pass, investigate, or send for the fog test.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure on an anti-fog coating

Baseline

Water contact angle when new

Why it matters: It shows whether the coating is hydrophilic enough to make condensation spread.

How to interpret: Published anti-fog coatings read below about 10°; set your gate from parts that passed your fog test.

When it is not enough: It does not predict time to fog on its own.

Durability

Angle after washing, wiping and abrasion

Why it matters: It shows whether anti-fog protection survives use.

How to interpret: Track the rise from new; a growing angle warns of fading performance.

When it is not enough: It does not show cosmetic damage or haze.

Ageing

Angle after storage and damp heat

Why it matters: Hydrophilic surfaces drift with contamination and ageing.

How to interpret: Compare with the same lot when new, measured the same way.

When it is not enough: It does not separate contamination from coating loss; reclean and remeasure.

Spreading

Angle over the first second

Why it matters: On superhydrophilic coatings the drop spreads within a second.

How to interpret: Read at a fixed early time and report it, as published work does.

When it is not enough: Very fast spreading can fall below what a single frame shows.

Validation

Validated measurement approach for anti-fog coatings

How the Dropometer itself has been validated, and how the check fits fog test standards.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

How it fits fog test standards

Eye protection standards test fogging on the finished part: EN 168 includes a test for resistance to fogging of oculars, ISO 18526-3 a test for fogging of lenses, ISO 16321-1 lists fogging as an optional requirement, and ANSI/ISEA Z87.1-2020 added anti-fog marking. None we found sets a contact angle limit. Contact angle tracks the surface behind those results through development and production.

Read the anti-fog science article
QC Protocol

How to check anti-fog coatings by contact angle

Six steps per coating. Repeat after each durability or ageing step.

1

Lock the method

Fix drop volume, read time and room conditions; hydrophilic coatings need an early, fixed read time.

3

Measure new coatings

Measure several spots on new samples and record the median.

4

Run durability steps

Wash, wipe, abrade or age samples by your protocol and measure after each step.

5

Set the gate

Set a contact angle gate from samples that passed and failed your fog test.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the anti-fog coating contact angle SOP

A two page SOP you can adapt for your coatings, with the method lock, durability and ageing steps, how to set a gate against your fog test, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Example output

Example anti-fog coating durability log

Example data only. Your values and gates will differ and must come from your own fog test results.

How to read this log

Example gate: at or below 15° after washing. Coating A stayed low through washing and abrasion. Coating B was low when new but rose after washing, matching its failed fog test. The spray kept the angle low only until the first wipe.

Sessile drop contact angle measurement: DI Water on Teflon surface, left contact angle 44.9°, right 45.7°

Example anti-fog coating durability log

Sample Treatment New (°) After 20 washes (°) After abrasion (°) Fog test
Uncoated None 82 82 83 Fail
A Permanent anti-fog coating 6 8 11 Pass
B Permanent anti-fog coating 7 24 31 Fail
C Anti-fog spray 9 65 70 Fail after wipe

Example data, not customer data. Polycarbonate lens samples; 2 µL water drops read at 0.5 s; median of 5 spots.

Signal order

The order to check signals on anti-fog coatings

Check these in order. Each one rules out a cause before you look at the next.

1

Method and timing

Rules out read time and drop size effects.

2

Uncoated reference

Confirms the measurement reads as before.

3

New coating angle

Shows the coating is hydrophilic enough.

4

Angle after durability

Shows whether anti-fog performance survives use.

FAQ

Common questions about anti-fog coatings

Questions anti-fog coating teams ask about contact angle and fog testing.

How do anti-fog coatings work?

Most attract water. Hydrophilic coatings lower the water contact angle, allowing the moisture to spread into a thin film instead of light scattering droplets, which keeps clear vision. Liu and colleagues reported a coating below 5° that showed no visible fog after 60 s over a hot water bath. Our article on the science of anti-fog coatings explains more.

What contact angle should an anti-fog coating have?

Published superhydrophilic anti-fog coatings read below 10°, many near 5°, though a packaging coating at 24° also kept film clear. No eye protection standard we found sets a contact angle limit, so set your own gate from samples that passed and failed the fog test your product uses, and measure at a fixed early read time.

Does a low contact angle guarantee anti-fog performance?

No. Contact angle tracks the surface, but fog tests also depend on coating thickness, water uptake and test conditions. Clean superhydrophilic surfaces can turn hydrophobic within hours from organic contamination. Use contact angle to screen and track coatings, and confirm with the fog test.

Which fog test standards apply?

For eye protection, EN 168 includes a test for resistance to fogging of oculars, EN 166 uses the N marking, ISO 18526-3 includes a test for resistance to fogging of lenses, ISO 16321-1 lists fogging as an optional requirement, and ANSI/ISEA Z87.1-2020 added an X anti-fog marking, since revised in 2025. ASTM F659 covers ski and snowboard goggles. Check the current edition your market uses.

Permanent anti-fog coating or anti-fog spray?

A permanent coating is bonded and cured on the part; sprays and wipes leave a temporary hydrophilic layer that wears off with wiping and washing. The advantages of anti-fog coatings that are permanent show up after use, and the benefits of anti-fog sprays are speed and low cost. Contact angle after a set number of wipes or washes shows the difference quickly, before a full fog test.

Do hydrophobic anti-fog surfaces exist?

Yes. Some approaches make droplets small and mobile so they roll away, rather than spreading them. For those, sliding angle matters as much as contact angle. Our sliding angle guide covers the method, and our page on hydrophobic coating performance covers repellent coatings.

How do you measure very low contact angles?

Use a small drop and read at a fixed early time, often within the first second, because the drop keeps spreading. Report the read time with every value. Measure flat witness samples coated with the lot where lenses are strongly curved.

Which instrument do we need?

One with fast image capture, small drops and fixed early read times. The Dropometer does this at the bench. Our consumer products guide covers eyewear, and our page on self cleaning and anti soiling covers related coated surfaces.

Business impact

What changes when you measure anti-fog coatings

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with anti-fog coating checks

Metric Before Dropometer With Dropometer Indicative Benchmark
Formulation screening Fog test on every candidate Contact angle first, fog test on the shortlist No published benchmark; track on your own projects
Durability Seen in customer complaints Angle tracked after washing and abrasion Angle held near 5° after boiling and abrasion (Liu et al., 2023)
Ageing Assumed stable Angle tracked over storage Rise to 13.8° after 50 days of ageing (Liu et al., 2023)
User acceptance Fogging reported in use Coatings that keep low angles chosen 88% of surveyed healthcare workers reported fogging (Agarwal et al., 2020)

See the measurement on your own coatings

Send new and worn coated samples. We will show the comparison on a call.

Book a 15 minute demo

Estimate avoided anti-fog rejects and recoats

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Anti-fog coating rework estimate

Estimate avoided rejects and recoats from anti-fog coating failures.

Each Dropometer unit is US$5,000; the default models one unit.
Your own average cost to strip, recoat or scrap one lot of coated parts.
No published benchmark. Contact angle catches surface problems, not every fog test failure; start low.
Scrap cost per event from anti-fog failures only, from your own records.

Result

~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = preventable rework cost + preventable scrap cost + other monthly savings.

Limits

What contact angle cannot tell you about an anti-fog coating

Honest limits, so you know when to reach for another test.

It is not a fog test and does not replace one.
Read time matters; hydrophilic drops spread fast.
Contamination raises the angle even on good coatings.
Curved lenses need flat witness samples.
Photocatalytic surfaces need defined UV light.
Hydrophobic anti-fog designs need sliding angle too.

Contact angle shows how water meets the coated surface and how use and ageing change it. Time to fog, light transmission, haze and optical quality need their own tests.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related coating workflows

These pages cover the anti-fog science, the contact angle standard for photocatalytic surfaces and related coating checks.

Standard

ISO 27448

Water contact angle on photocatalytic self cleaning surfaces.

View standard

Guide

The science of anti-fog coatings

How hydrophilic coatings keep surfaces clear.

Read guide

Related use case

Functional hydrophobicity and self cleaning

All hydrophobicity use cases in one place.

View Page

Related use case

PFAS free reformulation

Repellency without fluorinated chemistry.

View Page

Related use case

Hydrophobic coating performance verification

Checks on water repellent coatings.

View Page

Guide

Automotive guide

Surface science for automotive makers.

Read guide

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

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.

Contact us to report a correction
Sources

References

1.
Cebeci, F.C., Wu, Z., Zhai, L., Cohen, R.E., Rubner, M.F. Nanoporosity driven superhydrophilicity: a means to create multifunctional antifogging coatings. Langmuir 22(6):2856 to 2862, 2006. https://doi.org/10.1021/la053182p
2.
Liu, X., Xu, L., Zhao, S. et al. Double cross linked transparent superhydrophilic coating capable of anti fogging even after abrasion and boiling. RSC Advances 13:23409 to 23418, 2023. https://doi.org/10.1039/D3RA03113F
3.
Turkoglu et al. Polymers 14:4663, 2022. https://doi.org/10.3390/polym14214663
4.
Mounayer, Iline Vul, Margel. Molecules 29:958, 2024. https://doi.org/10.3390/molecules29050958
5.
Zhu et al. Polymers 17:599, 2025. https://doi.org/10.3390/polym17050599
6.
Zhu, K., Huang, Pruvost, Legrand, Pilon. Journal of Quantitative Spectroscopy and Radiative Transfer 194:98 to 107, 2017. https://doi.org/10.1016/j.jqsrt.2017.03.012
7.

Mills, A., Crow, M. International Journal of Photoenergy 2008:470670, 2008.

https://doi.org/10.1155/2008/470670
8.

Wang, R. et al. Light induced amphiphilic surfaces. Nature 388:431 to 432, 1997.

https://doi.org/10.1038/41233
9.

Agarwal, A., Agarwal, S., Motiani, P. Difficulties encountered while using PPE kits and how to overcome them: an Indian perspective. Cureus 12(11):e11652, 2020.

https://doi.org/10.7759/cureus.11652
10.

Introzzi, L. et al. Wetting enhancer pullulan coating for antifog packaging applications. ACS Applied Materials and Interfaces 4(7):3692 to 3700, 2012.

https://doi.org/10.1021/am300784n
11.

Mouterde, T. et al. Antifogging abilities of model nanotextures. Nature Materials 16(6):658 to 663, 2017.

https://doi.org/10.1038/nmat4868
12.

ISO 27448:2009. Fine ceramics: test method for self cleaning performance of semiconducting photocatalytic materials, measurement of water contact angle. See our ISO 27448 page.

https://www.iso.org/standard/53953.html
13.

EN 168:2001. Personal eye protection: non optical test methods.

https://shop.standards.ie/en-ie/standards/en-168-2001-345283_saig_cen_cen_789879/
14.

ISO 18526-3:2020. Eye and face protection: test methods, part 3, physical and mechanical properties (clause 6.11, resistance to fogging).

https://iteh.es/catalog/standards/sist/8d39fe6b-b2f7-48bd-9aa2-e739f6f29579/sist-en-iso-18526-3-2020
15.

ANSI/ISEA Z87.1-2020. Occupational and educational personal eye and face protection devices.

https://blog.ansi.org/2020/04/ansi-isea-z87-1-2020-safety-glasses-eye-face/
16.

ASTM F659. Standard specification for ski and snowboard goggles.

https://store.astm.org/f0659-10.html
17.

Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018.

https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
18.

Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects.

https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
19.
Droplet Lab validation papers
20.
Customer publications that cite the Dropometer
21.
The science of anti-fog coatings
22.
Contact angle measurement guide