Oxygen Transmission Rate (OTR) is the volume of oxygen gas that passes through one square meter of a film in 24 hours, expressed in cc/m²·24h; Water Vapor Transmission Rate (WVTR) is the mass of water vapor that passes through the same area in the same time, expressed in g/m²·24h — together they define how well a barrier film protects a packaged product from oxidation and moisture damage.
For converters buying metallized or coated barrier film by the roll, these two numbers on a technical data sheet (TDS) matter more than any marketing claim. A film with the wrong OTR lets roasted coffee go stale in weeks instead of months. A film with the wrong WVTR lets crackers go soft before the sell-by date. This guide breaks down what OTR and WVTR actually measure, how they are tested, how to read the numbers on a TDS, and which Expansteel barrier film grade fits which packaging application — using the real spec ranges published on our own TDS sheets, not generic marketing language.
OTR quantifies how much oxygen leaks through a film — the lower the number, the better the oxygen barrier.
Oxygen is the primary driver of lipid oxidation (rancidity in fats and oils), color fading, vitamin loss, and microbial growth in packaged food. OTR is reported as cc/m²·24h (sometimes written cm³/m²/day) at a specified temperature and relative humidity, because oxygen permeability through a polymer film changes with both variables. A metallized or aluminum-oxide (AlOx) coated film reduces OTR by orders of magnitude compared to uncoated PET or BOPP, which is why coating quality and adhesion — not just base film thickness — determine real-world barrier performance.
On Expansteel TDS sheets, OTR is always shown as a "≤" ceiling value (e.g., OTR ≤1.5 cc/m²·24h), meaning every roll tested is confirmed at or below that number, not merely averaging around it. This matters for converters running food-safety-critical lines where a single out-of-spec roll can compromise an entire production batch.
WVTR quantifies how much moisture migrates through a film — critical for crispness, caking, and shelf stability.
WVTR governs a different failure mode than OTR: moisture ingress (or egress) that causes crackers and chips to lose crunch, powders to cake, and dried goods to spoil. It is reported as g/m²·24h at a specified temperature and humidity gradient across the film. Because water vapor and oxygen move through polymer and coating layers via different mechanisms, a film can have an excellent OTR and a mediocre WVTR, or vice versa — which is why both numbers need to be checked independently against the product's actual failure risk, not assumed to move together.
Expansteel's barrier films report WVTR alongside OTR on every TDS specifically so converters do not have to guess which mechanism dominates for their product. For a vacuum-packed roasted coffee, oxygen is usually the bigger threat; for a hygroscopic powder or a crisp snack, moisture control often matters just as much or more.
Both values come from standardized ASTM instrument methods — knowing the method tells you how much to trust the number.
OTR is measured per ASTM D3985, "Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor." The film is mounted as a barrier between an oxygen-rich chamber and a nitrogen-purged chamber; oxygen that permeates through is carried to a coulometric detector, which produces a measurable electrical current proportional to oxygen flow. WVTR is measured per ASTM F1249, "Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor," where the film separates a wet chamber from a dry chamber and an infrared sensor tracks moisture crossing through.
Industry practice commonly runs OTR at 23°C / 0% RH and WVTR at 38°C / 90% RH — but conditions vary by lab and by buyer specification, so the temperature and humidity stated on any TDS (Expansteel's included) should always be checked before comparing two suppliers' numbers side by side. A film tested at 38°C/90% RH will always show a higher WVTR than the same film tested at 23°C/50% RH; that is a test-condition artifact, not a real performance difference.
| Parameter | Unit | Test Standard | Common Test Condition | What It Measures |
|---|---|---|---|---|
| OTR | cc/m²·24h | ASTM D3985 (coulometric sensor) | 23°C, 0% RH | Oxygen gas volume crossing 1 m² of film per day |
| WVTR | g/m²·24h | ASTM F1249 (modulated infrared sensor) | 38°C, 90% RH | Water vapor mass crossing 1 m² of film per day |
Three checks turn a TDS number into a usable engineering decision: the ceiling vs. typical value, the test condition, and the film thickness it was measured at.
First, check whether the OTR/WVTR figure is stated as a maximum ceiling ("≤") or a typical/average value. A ceiling spec is a QC commitment; a typical value is a marketing midpoint that individual rolls can exceed. Second, confirm the test temperature and humidity — as shown above, the same film can post very different WVTR numbers depending on whether it was tested at 23°C/50% RH or 38°C/90% RH, so only compare numbers measured under matching conditions. Third, note the film thickness the value was measured at; OTR and WVTR are area-based rates, not linear with thickness in a simple way once a metallized or AlOx coating is involved, so a thicker film is not automatically a better barrier — coating integrity and adhesion strength matter more than base film gauge.
Adhesion strength (reported in N/15mm) deserves equal attention alongside OTR/WVTR, because a coating that delaminates during lamination, printing, or pouch-forming will lose its barrier performance regardless of what the original TDS number said. All Expansteel barrier grades listed below are 12μm standard thickness and report aluminum or AlOx adhesion strength directly on the TDS for this reason.
Match your product's oxidation and moisture risk to a barrier range, then select the ES grade that meets it with margin — using Expansteel's own TDS ceiling values below.
Published barrier benchmarks vary by product category and by how conservative a brand wants to be, but the ranges below are commonly cited across packaging engineering references and give a practical starting point. Use them to shortlist a barrier tier, then confirm against your own shelf-life target and accelerated-aging test.
| Application | Typical Barrier Target | Recommended Expansteel Grade | Grade OTR / WVTR (≤, cc or g /m²·24h) |
|---|---|---|---|
| Snack foods, chips, moderate-barrier dry goods | OTR <3 / WVTR <2 | ES-GF | OTR ≤1.5 / WVTR ≤1.5 |
| Food-contact export packaging (FDA / EU 10-2011 compliance priority) | Same barrier class + verified regulatory compliance | ES-GF01 | OTR ≤0.8 / WVTR ≤0.8, Al adhesion ≥3.0 N/15mm |
| Roasted / ground coffee, oxidation-prone dry goods | OTR ≤0.5 (specialty-coffee benchmark) | ES-H01 | OTR ≤0.5 / WVTR ≤0.8 |
| Entry-tier coffee and oxidation-sensitive snacks | OTR ≤1.0 | ES-H | OTR ≤1.0 / WVTR ≤1.0, OD ≥1.5 |
| Extended shelf-life premium goods, light-sensitive products | Ultra-high barrier + high opacity for light block | ES-H03 (flagship) | OTR ≤0.1 / WVTR ≤0.3, OD ≥2.5, adhesion ≥2.5 N/15mm |
| Retort pouches, wet foods requiring 121°C sterilization | Barrier must survive thermal processing intact | ES-C01 | OTR 1.0 / WVTR 1.0, adhesion ≥4.0 N/15mm, 121°C/30min retort pass |
| Clear window packaging, consumer product visibility | High transmittance with moderate barrier | ES-T | OTR ≤2.0 / WVTR ≤2.0, transmittance ≥88% |
| Clear window pack requiring retort survivability | Transparent barrier through 121°C sterilization | ES-T01 | OTR ≤0.5 / WVTR ≤1.0, 121°C retort validated |
| Clear pack, ultra-high barrier and coating adhesion | Highest transparent barrier tier | ES-T03 | OTR ≤0.5 / WVTR ≤0.5, AlOx adhesion ≥5.0 N/15mm |
All grades above are supplied at 12μm standard thickness with full TDS documentation. The ES-GF series carries FDA, EU 10/2011, REACH, and RoHS food-contact compliance for converters exporting into regulated markets.
OTR measures oxygen gas permeation and governs oxidation, rancidity, and color/flavor degradation. WVTR measures water vapor permeation and governs moisture-driven failures like loss of crispness or caking. A film can score well on one and poorly on the other, so both should be checked against your product's specific spoilage mechanism rather than treated as a single combined "barrier" number.
Gas and vapor permeation through polymer and coating layers is temperature- and humidity-dependent by physical mechanism — higher temperature increases molecular mobility, and higher humidity can swell some polymer layers and increase permeability. That is why ASTM D3985 and ASTM F1249 specify controlled test conditions, and why two numbers are only directly comparable when tested under the same condition.
Not necessarily. An ultra-low-OTR film like ES-H03 (OTR ≤0.1) is the right choice for oxidation-sensitive, long-shelf-life goods, but it is over-specified — and typically higher cost — for a product that is more sensitive to moisture than oxygen, or that has a short intended shelf life. Match the grade to the actual failure mode and target shelf life, not to the lowest number on the sheet.
For metallized or AlOx-coated barrier films, the coating layer — not the base film thickness alone — does most of the barrier work, so OTR/WVTR does not scale simply with gauge. All Expansteel barrier grades in the table above are reported at 12μm standard thickness; requesting a different gauge from any supplier should come with a re-tested OTR/WVTR, not an assumption that thinner or thicker automatically shifts the number proportionally.
Only if the test standard and test condition match. Confirm both sheets cite ASTM D3985 (OTR) and ASTM F1249 (WVTR) and check the stated temperature/humidity before comparing figures — a WVTR measured at 38°C/90% RH will read higher than the same film measured at 23°C/50% RH, which can make an equal-performing film look worse purely due to test condition, not actual barrier quality.
OD (optical density) measures the aluminum coating's opacity and correlates with both light-blocking performance and, generally, oxygen barrier consistency — higher OD typically indicates a denser, more continuous metal layer. It is listed alongside OTR/WVTR on Expansteel TDS sheets (e.g., ES-H03 at OD ≥2.5) because for light-sensitive products, opacity is a second protection mechanism independent of the gas barrier numbers.
Data source: Expansteel TDS measurements, updated 2026-07.
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