Why Cellophane Breathes: Moisture Permeability Explained for Buyers

Why a buyer's bakery line cares whether the film breathes

A bakery packaging buyer in Manchester called us in February because the new film her line was running was trapping too much moisture inside the bag. The crust was going soft overnight. Her line had been converted from BOPP to a "compostable alternative" a few weeks earlier, and the supplier had not flagged the breathability change as part of the conversion. The bakery needed a film that breathes — and "compostable BOPP-replacement" turned out to be a film that did not.

This is the kind of question we see month after month. The buyer asks for "compostable," gets sent a cellulose-based film, and then has to learn what the new film does differently than BOPP in the same packaging context. One of the first things it does differently is breathe.

What "breathing" actually means, in polymer terms

In a packaging context, "breathable" almost always means moisture vapour permeable. Water molecules — H₂O in the gas phase — can pass through the film at a controlled rate, allowing the product inside to come to a moisture equilibrium with the environment outside. This is the opposite of what polyethylene, BOPP, and metal foils do: those films are essentially moisture barriers, holding water inside or keeping it out depending on which side of the gradient the humidity is higher.

Cellophane is moisture permeable because the cellulose backbone is hydrophilic. Water molecules hydrogen-bond with the hydroxyl groups on the cellulose chain, move through the film along polar pathways, and exit on the other side. The rate of transport depends on the relative humidity on each side, the temperature, the film's gauge, and the extent to which the film has been coated or pigmented. Cellophane is also permeable to a number of small gas molecules — oxygen, carbon dioxide — at rates that differ from polyolefins in ways that matter for specific applications (modified atmosphere packaging, for example).

BOPP and polyethylene, by contrast, are polyolefins — long hydrocarbon chains with no polar sites for water to hydrogen-bond to. Water molecules can move through them only by slow diffusion through amorphous regions of the polymer, and the resulting transmission rate is one to two orders of magnitude lower than for cellophane. That is exactly what the food industry wants when the goal is to keep water in (dried food) or keep water out (sensitive electronics). It is exactly what the bakery industry does not want when the goal is a crust that stays crisp.

How moisture permeability is measured — MVTR in one paragraph

The standard test is ASTM E96 (gravimetric) or ASTM F1249 (modulated atmosphere). Both report moisture vapour transmission rate (MVTR) in grams per square metre per 24 hours (g/m²/24h) at a defined temperature and relative humidity, typically 38 °C and 90% RH for the desiccant method or 23 °C / 50% RH for the water method. Lower MVTR = better moisture barrier; higher MVTR = more breathable.

The single number tells you a lot, but the test conditions matter as much as the result. A film measured at 38 °C / 90% RH is much more permeable than the same film at 23 °C / 50% RH — moisture permeability roughly triples for every 10 °C of temperature increase, and it increases non-linearly with humidity. Ask the supplier for MVTR at the conditions your warehouse and supply chain actually run at, not just the headline number on the datasheet.

Cellophane vs BOPP vs PE vs PLA — at one set of conditions

The comparison below is illustrative; actual MVTR varies with gauge, formulation, and coating system. Numbers are in g/m²/24h for a 25 µm film at 38 °C / 90% RH.

If the conversion from BOPP to "compostable" caught the Manchester bakery by surprise, the table above is what shifted. BOPP's near-zero MVTR was holding the crust dry by trapping the bread's own moisture inside a sealed bag; cellophane's higher MVTR was releasing that moisture before it condensed back into the crumb. Switching films without re-tuning the line and the bag's headspace is the kind of conversion mistake that takes a week to discover.

How coatings tune cellophane between breathable and barrier film

The unique property of cellophane as a packaging film is that its breathability is tuneable by what is put on top of it. The underlying substrate stays the same; the coating system is what changes the permeability.

Our coated cellulose film range delivers three configurations from the same substrate chemistry. Uncoated regenerated cellulose gives the highest MVTR and is the right choice for applications where breathability is desired — bakery, fresh produce, certain cheeses. Single-side coated reduces MVTR by roughly half and gives one breathable face plus one barrier face — useful where one side of the bag sits against moisture-sensitive product and the other faces out. Two-sides coated drops MVTR significantly and is the right choice for products that need barrier behaviour compatible with compostability, like dried fruit or snack foods.

For products that need a near-metal barrier, our aluminised cellulose film delivers MVTR below a few g/m²/24h while keeping the substrate chemistry as cellulose. This is the high-barrier edge of the cellophane family — at this point the film is no longer "breathable" by any meaningful definition, but it remains bio-based at the polymer level and industrially compostable if the laminate stays simple.

Where breathability is the feature — and where it is a problem

The breathability question comes up in five application families that come to our desk. The match-mismatch with cellophane is straightforward once you understand the mechanism.

• Fresh bakery. Match. The moisture that escapes through the film is what keeps the crust crisp. Coated cellophane gives a touch of moisture retention if the product is wetter (e.g., filled pastries).
• Cheese. Match (depending on cheese type). Bloomy-rind cheeses want some gas exchange; harder cheeses can tolerate more barrier.
• Fresh produce. Match. Cellophane's breathability lets ethylene diffuse out and helps delay senescence. Pre-punched or micro-perforated PE is the petrochemical alternative.
• Dried fruit, snack foods, coffee. Mismatch. These products need barrier, not breathability. Two-sides coated cellophane or aluminised cellulose is the cellulose-based option; BOPP and metallised films are the petrochemical alternative.
• Pharmaceutical overwrap. Mixed. Tablets, capsules, and diagnostic strips vary in their sensitivity; the spec has to be matched to the specific product, not to "pharmaceutical" as a category.

Common mistakes buyers make on breathability — and what to do instead

A short buyer-side checklist of the patterns I see repeatedly on procurement calls. Use it to pressure-test your supplier before signing off on the spec.

1. Reading MVTR at the wrong condition. "High MVTR" at 38 °C / 90% RH is not the same number as at 23 °C / 50% RH. Pick the condition your supply chain actually runs at and ask for that number.
2. Confusing moisture permeability with oxygen permeability. OTR (oxygen transmission rate) and MVTR are different measurements; a breathable film can be a good oxygen barrier or a poor one. For snack foods, the oxygen number matters more than the moisture number.
3. Treating uncoated cellophane as the universal baseline. Cellophane's MVTR depends strongly on the coating system. Quoting an "MVTR of cellophane" without naming the coating is meaningless.
4. Forgetting about creep at high humidity. At sustained high humidity, hydrophilic films absorb some water and their gauge increases — which changes the MVTR. If your supply chain includes tropical or humid warehousing, ask the supplier for humidity-conditioned MVTR data.
5. Specifying breathability for a product that needs barrier. The Manchester bakery case in reverse — a product that wants barrier can be ruined by an overly breathable wrap. Match the breathability to the product, not to the sustainability claim.

Five buyer-side checkpoints before commit

1. MVTR at your conditions. Ask the supplier for MVTR measured at the temperature and RH your supply chain will actually run at, not a generic number.
2. Coating system identified. The spec should name the coating — nitrocellulose, vinyl copolymer, PVdC-free, or aluminised — and the supplier's test report should match.
3. OTR data for oxygen-sensitive applications. If the product is moisture-sensitive or shelf-life sensitive, request OTR at the same gauge as well.
4. Sample retention clause. Hold a 1 m² reference sample from the first received lot and compare against incoming samples over the supplier relationship.
5. End-of-life claim, anchored to certification. ASTM D6400 and EN 13432 industrial composting thresholds are the reference. For independent supply-chain verification, third-party testing bodies such as Intertek run moisture vapour transmission rate (MVTR) and oxygen transmission rate (OTR) tests to provide the auditable data behind supplier claims. The BPI directory lists certified grades.

For buyers who want to start with the breathable side of the cellophane range, our regenerated cellulose film reels and sheets cover the uncoated grades, and our coated cellulose film covers the tunable barrier side. For applications that need a near-metal high barrier with cellulose substrate chemistry, our aluminised cellulose films deliver below-a-few-g/m²/24h MVTR. The broader cellulose-fibre and barrier-film landscape is covered by industry publications including Chemical & Engineering News. To request a specification sheet tailored to your product and your supply chain, contact our technical team.

Frequently asked questions

About the author

© 2026 Zhejiang Xiade New Material Co., Ltd. (XIADE). All rights reserved. This article is intended for B2B buyers and packaging specifiers. MVTR values referenced are illustrative and depend on gauge, formulation, coating system, and test conditions — request supplier data on the specific grade and your specific supply-chain conditions.