Direct Answer
OTR and WVTR are the two transmission measurements that decide whether packaging protects a product from oxidation and moisture. OTR is the oxygen transmission rate and WVTR is the water vapor transmission rate, each measured under controlled conditions with a named method, so the conditions and the method must travel with the number. Reading a barrier data sheet correctly means checking the method, temperature, and relative humidity first, then checking whether the value is for flat material or a formed pack, because a flat-sheet value describes the substrate and not the finished pack. Set the specification by stating the OTR and WVTR limits the product needs, the method, and the conditions, then verify on the formed pack.
Opening Hook
A coffee roaster switched to a coated fibre bag, compared the supplier's WVTR against its previous film, and only later found the two numbers had been measured at different relative humidity levels and one was for flat material while the other was for a formed bag. The comparison had been wrong at the level of the test conditions, and the coffee went stale faster than the sheet promised. The numbers were accurate; the comparison was not. At ecosora, we read OTR and WVTR by their method and conditions first, because a transmission number without its conditions is a guess wearing a decimal point.
What the Two Measurements Mean
| Measurement | What It Tracks | Product It Protects |
|---|---|---|
| OTR (oxygen) | Oxygen ingress | Oxidation, rancidity, aroma loss |
| WVTR (moisture) | Water vapor ingress | Staling, clumping, drying out |
| Seal integrity | Closure leakage | Both, at the seal |
| Grease resistance | Oil and fat | Fatty foods |
OTR and WVTR are the two headline barrier numbers, but they are joined by seal integrity and grease resistance for many products. A format can have an excellent substrate OTR and still fail on a weak seal, which is why the formed pack, not the sheet, is the thing that matters for a real product.
Data: ASTM International publishes oxygen and water vapor transmission test methods that let a brand measure OTR and WVTR under controlled conditions on a shared measurement basis.
Judgment: Require the named method and test conditions behind any barrier number, because a transmission value without its method and conditions cannot be repeated or compared.
Source: ASTM International — ASTM Standards (2024)
Test Methods and Conditions
| Element | What to State | Why It Matters |
|---|---|---|
| Test method | ASTM or ISO method name | Repeatability |
| Temperature | Test temperature | Transmission changes with heat |
| Relative humidity | Test RH | WVTR is RH-dependent |
| Sample form | Flat vs formed | Substrate vs pack |
| Acceptance limit | Target value | Defines pass/fail |
Every element belongs in the specification, because transmission values are condition-dependent and the conditions decide what the number means. Two WVTR numbers measured at different relative humidity are not comparable, and a flat-sheet OTR is not the same as a formed-pack OTR. State the method, the conditions, and the sample form before you compare.
Flat Sheet vs Formed Pack
| Sample Form | What It Measures | What It Misses |
|---|---|---|
| Flat material | Substrate barrier | Seals, folds, corners |
| Formed pack | Real geometry | Nothing structural |
| Sealed pouch | Pack plus seal | Nothing structural |
| Coated vs uncoated | Coating contribution | Process variation |
The flat-versus-formed gap is the most common source of a barrier surprise, because a substrate value describes the material while the product sits in a formed pack with seals and corners that transmit differently. Use the flat value to screen candidates, then verify on the formed pack. Where a food-contact safety check runs alongside, the barrier and safety evidence share the same formed sample.
Setting the Barrier Specification
| Spec Element | What It Contains |
|---|---|
| OTR limit | Max oxygen transmission allowed |
| WVTR limit | Max moisture transmission allowed |
| Method | Named test standard |
| Conditions | Temperature and humidity |
| Sample form | Formed pack, not sheet |
The specification converts a product need into a measurable, verifiable requirement. The limit comes from the product's sensitivity — how much oxygen or moisture it can tolerate before it fails — not from what a material family typically achieves. Writing the method and the acceptance limit into the spec is what turns a disputed barrier result into a shared finding.
Data: ISO's standards catalogue covers the barrier and transmission test standards that OTR and WVTR specifications draw on, giving a common language between brand and supplier.
Judgment: Write the method and acceptance limit into the specification, because an agreed method and limit are what make a barrier number enforceable in a supply relationship.
Source: ISO — ISO Standards Catalogue (2024)
Common Barrier Testing Mistakes
| Mistake | Consequence | Prevention |
|---|---|---|
| Comparing different conditions | Invalid comparison | Fix one condition set |
| Flat vs formed mix-up | Wrong conclusion | State sample form |
| Method not named | Unrepeatable number | Require method |
| No acceptance limit | No pass/fail | Set the limit |
| Seal untested | Hidden leakage | Test the formed pack |
Each mistake is a measurement or specification gap rather than a material failure, so it is avoidable before the test runs. Fix the conditions, name the method, state the sample form, set the limit, and test the seal, and the barrier number becomes a decision tool instead of a source of confusion.
A Barrier Verification Workflow
| Step | Action | Output |
|---|---|---|
| Define need | State product OTR and WVTR limits | Spec basis |
| Screen | Compare substrate values | Shortlist |
| Verify | Test formed packs | Real result |
| Confirm | Run shelf-life check | Product behavior |
| Monitor | Lot-to-lot checks | Continued conformance |
The workflow moves from the product's need to the formed pack's verified performance, with the substrate used only for screening. Where the format overlaps with a mono-material packaging change, the barrier spec is the check that confirms the material swap did not quietly reduce protection.
Data: TAPPI publishes technical resources on paper and packaging barrier properties, including the material and coating data that OTR and WVTR performance depends on for fibre-based formats.
Judgment: Anchor barrier expectations to the material's technical data and the coating system, because a fibre format's OTR and WVTR are set by the substrate and coating, not by intent.
Source: TAPPI — Paper and Packaging Technical Resources (2024)
The Bottom Line
OTR and WVTR decide whether packaging protects the product, so state the limits the product needs, name the method and conditions, and verify on the formed pack rather than the sheet. In one sentence: ecosora reads OTR and WVTR by their method and conditions and verifies on the formed pack, so a barrier number never overpromises what the pack delivers.