Functional Hydrophobicity

Biodegradable Packaging Films for Food Packaging: Measure the Water Resistance of Each Biodegradable Film Before It Meets the Food Product

Most biodegradable food packaging films are hydrophilic and change when water sits on them. Measure water contact angle on the film surface, at a fixed time and over time, to rank formulations and release batches alongside water vapor and solubility tests.

Who this is for: Packaging researchers, film developers and quality teams working on biodegradable and compostable food packaging films.

Where it fits: Formulation screening, coating and additive selection, and batch release of packaging film.

What it does not do: It does not measure water vapor permeability, oxygen barrier, solubility or compostability.

Method

Sessile drop water contact angle, read at fixed times; surface free energy with a second liquid

Standard

Fully compliant with ISO 19403-2 for surface free energy; complements AATCC TM22 spray testing

Setup

About 2 minutes

Book a 15 minute demo Request a quote

Written by

Abhimanyu Bhandankar

Holds an MBA from Schulich School of Business and a BE in IT. He joined Droplet Lab in July 2019 and now leads sales and marketing.

CEO at Droplet Lab

Why water resistance decides biodegradable packaging

78 million tonnes

of plastic packaging were put on the market in 2013, and only 14% was collected for recycling.

Ellen MacArthur Foundation, The New Plastics Economy, 2016

76° to 120°

rise in PLA film water contact angle after a hydrophobic plasma treatment, which improved the water barrier by only about 17%.

Tenn et al., RSC Advances 4(11):5626, 2014

8 minutes

of monitoring drops on five biopolymer coatings showed a water contact angle equilibrium does not apply to most biopolymers; most change came in the first 60 s.

Farris et al., Langmuir 27(12):7563, 2011

Sources: Ellen MacArthur Foundation, The New Plastics Economy: Rethinking the future of plastics, 2016; Tenn N. et al., Impact of hydrophobic plasma treatments on the barrier properties of poly(lactic acid) films, RSC Advances, 2014; Farris S. et al., Wetting of biopolymer coatings: contact angle kinetics and image analysis investigation, Langmuir, 2011. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this water resistance check does and what it does not

A quick reference for packaging teams checking fit before reading further.

Evidence Box

Problem this solves

Packaging made with biodegradable films that soften, swell or let moisture through once they meet a wet or fresh food product.

Standards

Fully compliant with ISO 19403-2 for surface free energy; complements AATCC TM22 spray testing and water vapor tests such as ASTM E96.

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

A South Dakota State University food science lab made water contact angle a standard test for its crop waste packaging films and reported it in seven papers.

Published research

Optimized soyhull and corncob residue films read 72.6° and 63.4° water contact angle in Food Chemistry (2024), both hydrophilic by the authors' 90° criterion.

Honest limit

Contact angle measures the surface only. A film can read well and still pass moisture through its bulk.

Who this is for

What packaging film 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.

R&D film developer

You are developing biodegradable films from biopolymers, crop residues or blends for flexible packaging or thin film wraps, and need to know which formulation resists water best. Contact angle at fixed times ranks candidates in minutes, before longer water vapor and solubility tests.

Condition films at a set humidity first; biopolymer films change with moisture.

Packaging quality manager

Your plant makes biodegradable packaging film or coated paper for food packaging applications in the food industry. A contact angle gate set from an approved reference gives each batch a recorded release decision.

Measure the side that faces the food product; cast and air sides can differ.

Coating and process engineer

You add a hydrophobic coating, wax or additive, or active food packaging agents, to a food packaging application and need to keep moisture resistance. Measuring before and after shows what the coating changed, and whether drying or cure is consistent.

A higher surface angle does not prove a better water vapor barrier.

Fit check

Is this the right test for your biodegradable packaging film?

It measures how water meets the film surface. It does not measure what passes through the film.

Good fit if

You compare biodegradable film formulations, blends or composite film options.

You add coatings, waxes or additives to improve water resistance.

You need to see how fast water soaks into or swells the film.

You release packaging film batches against a reference.

You report water contact angle in papers on materials for food packaging or in customer data sheets.

Less relevant if

You need water vapor or oxygen transmission rates.

You need water solubility, swelling or compostability results.

You need a textile spray rating as written in AATCC TM22.

You need food contact or migration approval.

Summary

How to measure water resistance of biodegradable packaging film

The answer in under a minute.

Condition the film, place a water drop on the side that faces the food, and read the contact angle at a fixed early time and again later. The early angle shows surface water resistance; the drop over time shows how fast water soaks in. Use both, with water vapor and solubility tests, to rank formulations and release batches.

The Dropometer contact angle kit runs the test; our contact angle measurement guide explains the method. A South Dakota State University food science lab reports it across seven papers, including soyhull residue films for raspberries and corncob residue films. A Cornell University fiber lab showed lignin makes PLA fiber mats more water repellent. Our packaging and containers guide covers the wider context.

Expert Quote

Expert perspective on water repellency

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.

The problem

Why biodegradable films struggle with water

Biodegradable packaging is replacing conventional plastic packaging in food packaging applications, driven by plastic waste: 78 million tonnes of plastic packaging reached the market in 2013 and only 14% was collected for recycling. Biodegradable films made from starch, cellulose, chitosan, carrageenan, proteins and crop residues are attractive biodegradable materials, but most are hydrophilic. Their polar groups attract water, so the film can soften, swell or lose strength when it meets a moist food product, and its barrier properties suffer. Many published biodegradable packaging films read below 90° water contact angle, and on most biopolymers the angle keeps changing as water spreads and soaks in, so a single reading taken at a random moment is not comparable. Teams add lignin, waxes, lipids, crosslinkers or hydrophobic coatings, or build a multilayer film, to improve moisture resistance. A biodegradable material must also break down in an industrial compost environment under EN 13432 or ASTM D6400, so hydrophobic additives cannot simply be borrowed from conventional plastic packaging. Food waste matters too: the packaging industry needs a sustainable packaging solution that still protects food quality. Each change needs a quick, repeatable surface test alongside the slower water vapor, solubility and swelling tests that decide whether the film protects the food.

Films soften, wrinkle or lose strength when in contact with a moist food product.

Water drops spread or soak in within seconds on the film surface.

Results change with room humidity or storage time.

Coated and uncoated sides behave differently.

Batches of the same formulation give different water resistance.

Troubleshooting

Why biodegradable packaging films lose water resistance

Why:

Polysaccharides and proteins carry hydroxyl and other polar groups that attract water.

How to detect:

A low early contact angle, often below 90°, on the uncoated film.

Corrective action:

Blend in a more hydrophobic polymer, add lignin or a lipid, or apply a hydrophobic coating, then remeasure.

Why:

Plasticisers and some blend partners make films more hydrophilic. In one alfalfa residue and carrageenan study, adding carrageenan lowered water contact angle from 74.7° to 60.9°.

How to detect:

The angle falls as the additive level rises.

Corrective action:

Find the additive level where mechanical gains stop outweighing water resistance losses.

Why:

Water absorbs into hygroscopic films, so the drop shrinks and the angle falls with time.

How to detect:

A large drop in angle between the early and later readings.

Corrective action:

Check crosslinking and drying, and confirm with water solubility and swelling tests.

Why:

Biopolymer films take up moisture from the air, which changes their surface.

How to detect:

Readings drift with the day's humidity.

Corrective action:

Condition films at a set humidity and time before testing. Our guide to reproducible contact angle measurement covers fair comparisons.

Why:

Cast films and coated films often have two different sides.

How to detect:

Readings differ between sides or across the sheet.

Corrective action:

Mark and test the side that faces the food product, at several spots.

Why:

Texture changes the apparent angle, so a rough or fibrous film can read high without better chemistry. Our Cassie Baxter model glossary entry and experiment on superhydrophobic glass explain why.

How to detect:

High angles on fibrous mats or rough films that still absorb water.

Corrective action:

Compare with a smooth reference and check whether drops roll off; our sliding angle guide covers that test.

Not sure why your film is losing water resistance?

Bring a reference film and a problem batch to a call, and we will compare them on screen.

Book a 15 minute demo

Quality records

What a packaging film water resistance record contains

Each check produces a record you can file with the film batch or formulation. These records can feed into your existing quality records and customer data sheets.

Film identity

Formulation, batch, thickness, coating and the side tested.

Conditioning

Humidity and time before testing, and room temperature and humidity during it.

Method settings

Drop volume, reading times and drops per film.

Readings

Early and later contact angles, median and spread, and the drop over time.

Decision

Release, retest or hold, with links to water vapor and solubility results.

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 for barrier properties and water resistance

Surface

Early water contact angle

Why it matters: It shows how strongly the film surface resists water.

How to interpret: Compare with your reference film. Thresholds are set per film type from your own correlation with product trials; many papers use 90° to separate hydrophilic from hydrophobic.

When it is not enough: It does not show what passes through the film.

Time

Contact angle change over time

Why it matters: It shows absorption and swelling, the main water problem for biopolymer films.

How to interpret: A large fall between readings means water soaks in quickly.

When it is not enough: Evaporation also shrinks drops; keep humidity steady.

Surface energy

Surface free energy with a second liquid

Why it matters: It shows polar and dispersive parts, which matter for printing, sealing and coating the film.

How to interpret: Use the same liquids and model for every film.

When it is not enough: Absorbing films can make values unreliable.

Barrier

Water vapor permeability, measured separately

Why it matters: This is the barrier property that protects the food product.

How to interpret: Use a gravimetric cup method such as ASTM E96.

When it is not enough: The Dropometer does not measure it.

Validation

Validated measurement approach for packaging films

How the Dropometer itself has been validated, and where packaging researchers have used it to study the properties of biodegradable films.

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

Customer evidence in biodegradable packaging

Since September 2023, Prof. Srinivas Janaswamy's group at South Dakota State University has used a Dropometer to measure water contact angle on films made from corncob, soyhull, alfalfa and wheat straw residues, reported in seven papers from 2024 to 2026.

Read the case study

QC Protocol

How to test the water resistance of a biodegradable film

Six steps for one film type. Repeat for each new formulation or coating.

1

Condition the film

Store samples at a set humidity and time; biopolymer films change with moisture.

2

Lock the method

Fix drop volume, the two reading times, drops per film and the side tested.

3

Measure the reference

Measure your approved film, and check readings against our Droplet Lab reference measurements dataset.

4

Set gates from product tests

Correlate early angle and drop over time with water vapor, solubility and product trial results.

5

Measure each formulation or batch

Measure the same way and compare with the reference on the same day.

6

Release, retest or hold

Release films inside the gates. Our guide to the best contact angle goniometer for industrial QA covers production use.

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 packaging film water contact angle SOP

A two page SOP you can adapt for your films, with the method lock, conditioning, gates against a reference, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Example output

Example screen of biodegradable film formulations

Example data only. Your values and gates will differ and must come from your own reference films.

How to read this screen

Example gates: early contact angle at or above 75° and a drop of no more than 10° by 60 s. The plasticised film starts lower and falls fastest, so water soaks in. The wax coated film starts highest and holds. The fibrous mat reads high, but its fall over time shows the texture, not the chemistry, is doing the work.

Example biodegradable film screen

Film	Change	Contact angle at 5 s (°)	Contact angle at 60 s (°)	Drop over time (°)	Result
Reference cellulose residue film	Approved	78	71	7	Reference
Plus 20% plasticiser	More glycerol	66	48	18	Hold
Plus wax coating	Coated side	96	93	3	Release
Plus carrageenan	Blend partner	70	60	10	Retest
Electrospun fiber mat	Fibrous texture	112	85	27	Check texture

Example data, not customer data. Films conditioned 48 h at 50 %RH, 23 °C; 4 µL water drops on the food contact side; readings at 5 s and 60 s.

Signal order

The order to check signals when a film fails on water

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

1

Conditioning and humidity

Rules out moisture differences before testing.

2

Side and spot

Confirms you measured the food contact side at fair spots.

3

Early contact angle

Shows surface water resistance against the reference.

4

Drop over time

Shows absorption and swelling.

5

Water vapor and solubility

Confirms the barrier itself; see our food and beverages guide for food side context.

FAQ

Common questions about biodegradable packaging films and water

Questions packaging researchers and quality teams ask about water resistance.

There is no single target. Many papers call a film hydrophilic below 90° and hydrophobic above it, and untreated PLA reads about 76°. Set your own gate from a reference film that performed well in water vapor, solubility and product trials, and measure every film the same way.

Water spreads into and is absorbed by most biopolymers. Farris and colleagues (Langmuir, 2011) found a water contact angle equilibrium does not apply to most biopolymer coatings, with most change in the first 60 seconds. Read at fixed times, and report the drop over time as a result in its own right.

Not necessarily. Tenn and colleagues (RSC Advances, 2014) raised the water contact angle of PLA film from 76° to 120° with plasma, yet water permeability improved by only about 17%. Contact angle measures the surface; water vapor transmission depends on the whole film. Measure both.

ASTM E96 covers water vapor transmission of materials, and ASTM D5946 covers water contact angle on corona treated polymer films. EN 13432 and ASTM D6400 cover compostability. AATCC TM22 is a textile spray test that contact angle complements. Surface free energy follows ISO 19403-2.

They can. In a Harvard University study of chitosan and silk fibroin laminates, wax coatings raised the mean water contact angle to 81°, 35% above the untreated chitosan layer. Check that the coating keeps the film compostable, and confirm the gain with water vapor tests.

Lignin is less hydrophilic than cellulose and is often added for that reason. A Cornell University fiber lab found lignin made electrospun PLA mats more water repellent, with results that depended on where the lignin came from and how it was isolated.

Materials used include biodegradable polymer families such as PLA, PHA and PBS, and biopolymer films from starch, cellulose, chitosan, carrageenan, proteins and crop residues; an edible film is a special case eaten with the food. Many are made as a composite film, nanocomposite films or a multilayer film to balance film properties such as strength and the barrier to oxygen and water. Water contact angle belongs in the development of biodegradable films from the first trial.

A contact angle instrument that reads at fixed times, records drop images, and calculates surface free energy with a second liquid. Our guide to the best contact angle goniometer for industrial QA compares options, and our edible coatings page covers coatings applied directly to food.

Business impact

What changes when you measure film water resistance

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

Before and with water contact angle checks

Metric	Before Dropometer	With Dropometer	Indicative Benchmark
Formulation screening	Water vapor and solubility tests only	Contact angle at fixed times first, then the slower tests	No published benchmark; track on your own formulations
Coating decisions	Visual drop test	Contact angle before and after coating	PLA 76° to 120° gave only about 17% better water barrier (Tenn et al., 2014)
Comparable readings	One reading at an unknown time	Fixed reading times and drop over time	Equilibrium angle does not apply to most biopolymers (Farris et al., 2011)
Batch release	Visual or none	Contact angle gate from the reference film	No published benchmark; track on your own batches

See the test on your own films

Send a reference film and a candidate. We will show the comparison on a call.

Book a 15 minute demo

Estimate saved film development work

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

Instrument cost ($) Each Dropometer unit is US$5,000; the default models one unit.

Film formulations tested per month

Material cost per formulation ($) Materials, casting and barrier testing cost for one film formulation.

Technician hours per formulation Film casting, conditioning, contact angle and analysis.

Loaded lab rate ($/hr)

Film formulations you expect to screen out earlier (%) No published benchmark. Use your own estimate and start low if unsure.

Result

~0

Formulations saved per month

~0

Monthly savings

~0

Payback period

~0

First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What contact angle cannot tell you about packaging film

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

It does not measure water vapor or oxygen transmission.

Absorbing films change during the reading; fix the reading times.

Humidity changes biopolymer films; condition before testing.

Rough or fibrous films can read high without better chemistry.

Surface free energy is unreliable on films that absorb the probe liquids.

It does not show whether a biodegradable plastic is fully biodegradable, compostable or approved for food contact.

Water contact angle shows how the film surface meets water and how fast water soaks in. Water vapor and oxygen barrier, solubility, strength, compostability and food contact approval need their own tests.

Book a 15 minute demo Request a quote

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.

Ellen MacArthur Foundation. The New Plastics Economy: Rethinking the future of plastics. 2016. https://www.ellenmacarthurfoundation.org/the-new-plastics-economy-rethinking-the-future-of-plastics

2.

Tenn, N. et al. Impact of hydrophobic plasma treatments on the barrier properties of poly(lactic acid) films. RSC Advances 4(11):5626, 2014. https://doi.org/10.1039/c3ra45323e

3.

Farris, S. et al. Wetting of biopolymer coatings: contact angle kinetics and image analysis investigation. Langmuir 27(12):7563 to 7574, 2011. https://doi.org/10.1021/la2017006

4.

ASTM E96/E96M. Standard test methods for gravimetric determination of water vapor transmission rate of materials. https://store.astm.org/e0096_e0096m-24.html

5.

ASTM D5946-24. Standard test method for corona treated polymer films using water contact angle measurements. https://store.astm.org/d5946-24.html

6.

EN 13432:2000. Packaging: requirements for packaging recoverable through composting and biodegradation. https://www.dinmedia.de/en/standard/din-en-13432/32115376

7.

Regmi, S., Janaswamy, S. Biodegradable films from soyhull cellulosic residue with UV protection and antioxidant properties improve the shelf life of post harvested raspberries. Food Chemistry 460:140672, 2024. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/biodegradable-films-from-soyhull-cellulosic-residue-with-uv-protection-and-antioxidant-properties-improve-the-shelf-life-of-post-harvested-raspberries/

8.

Paudel, S., Janaswamy, S. Corncob derived biodegradable packaging films: a sustainable solution for raspberry post harvest preservation. Food Chemistry 454, 2024. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/corncob-derived-biodegradable-packaging-films-a-sustainable-solution-for-raspberry-post-harvest-preservation/

9.

Paudel, S., Janaswamy, S. Biodegradable films based on alfalfa cellulosic residue and carrageenan blends for sustainable food packaging. Sustainable Food Technology, 2026. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/biodegradable-films-based-on-alfalfa-cellulosic-residue-and-carrageenan-blends-for-sustainable-food-packaging/

10.

Szlek, D., Fan, Frey, M. Multifunctional, flexible, electrospun lignin and PLA micro and nanofiber mats. Fibers 13:129, 2025. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/multifunctional-flexible-electrospun-lignin-pla-micro-nanofiber-mats-from-softwood-kraft-hardwood-alcell-and-switchgrass-celf-lignin-2/

11.

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

12.

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

13.

Droplet Lab validation papers

14.

Customer publications that cite the Dropometer

15.

South Dakota State University case study

16.

Eco-friendly packaging films from soyhull lignocellulose analysis

17.

Chitosan and silk fibroin laminates analysis

Biodegradable Packaging Films for Food Packaging: Measure the Water Resistance of Each Biodegradable Film Before It Meets the Food Product

Abhimanyu Bhandankar

Droplet Lab Team

Featured Studies & Publications

Why water resistance decides biodegradable packaging

78 million tonnes

76° to 120°

8 minutes

What this water resistance check does and what it does not

Evidence Box

What packaging film question are you trying to answer?

R&D film developer

Packaging quality manager

Coating and process engineer

Is this the right test for your biodegradable packaging film?

Good fit if

Less relevant if

How to measure water resistance of biodegradable packaging film

Expert perspective on water repellency

Why biodegradable films struggle with water

Why biodegradable packaging films lose water resistance

Not sure why your film is losing water resistance?

What a packaging film water resistance record contains

Film identity

Conditioning

Method settings

Readings

Decision

Drop images

What to measure for barrier properties and water resistance

Early water contact angle

Contact angle change over time

Surface free energy with a second liquid

Water vapor permeability, measured separately

Validated measurement approach for packaging films

How to test the water resistance of a biodegradable film

Condition the film

Lock the method

Measure the reference

Set gates from product tests

Measure each formulation or batch

Release, retest or hold

Download the packaging film water contact angle SOP

Example screen of biodegradable film formulations

Example biodegradable film screen

The order to check signals when a film fails on water

Conditioning and humidity

Side and spot

Early contact angle

Drop over time

Water vapor and solubility

Common questions about biodegradable packaging films and water

What changes when you measure film water resistance

Before and with water contact angle checks

See the test on your own films

Estimate saved film development work

Estimate saved film development work.

What contact angle cannot tell you about packaging film

Standards, evidence and related water resistance workflows

AATCC TM22

South Dakota State University

Cornell University

Harvard University

Alfalfa residue and carrageenan films

Chitosan and silk fibroin laminates

Dropometer

Functional hydrophobicity and self cleaning

Edible coatings on fresh produce

High voltage insulator hydrophobicity

How this page was created

Drafting assistance

Technical review

Verification steps

Updates

Report a correction

References