TL;DR: Switching a premium snack brand from metal tins to composite cans cut packaging cost by 31% while maintaining the same shelf barrier life — but only after we resolved a wall delamination problem that appeared on the third production run.
TL;DR: The validated composite can specification for this project used a 3-ply body wall at 1.8mm total caliper, with a 25 µm LDPE moisture barrier laminate and a foil inner liner achieving WVTR below 0.8 g/m²/day.
From Metal Tin to Composite Can: A 14-Month Transition Case Study #
This project started as a cost-reduction brief from a UK-based premium snack brand. Their existing tin was performing well on shelf — seals were good, graphics were sharp — but the unit cost at their 180,000-unit annual volume was making the SKU economics difficult. The brief to our team was straightforward: find a composite can solution that matches the tin on barrier performance and premium shelf appearance, at a lower landed cost.
We’ve run this category of conversion project roughly eight times in the past four years, mostly in the snack, tea, and coffee segments. The outcome is rarely as simple as “swap the format.” This one was no exception.
The target specification we agreed before sampling:
| Parameter | Metal Tin (Baseline) | Target Composite Can | Achieved Composite Can |
|---|---|---|---|
| Wall thickness | 0.22mm tinplate | 1.8mm (3-ply paper/PE/foil) | 1.82mm ±0.05mm |
| WVTR (38°C/90% RH) | <0.5 g/m²/day | <1.0 g/m²/day | 0.72 g/m²/day |
| Drop resistance (1.2m) | Pass | Pass | Pass (8/10 units) |
| Unit cost (FOB Shenzhen) | Index 100 | Index 65–70 | Index 69 |
| Lead time (production) | 35 working days | 25–30 working days | 27 working days |
The WVTR target was set at <1.0 g/m²/day based on shelf-life modelling the brand’s R&D team had done for their nut snack product — 12-month ambient shelf life at up to 75% RH retail environments. ASTM E96 Method B was the test method specified throughout, which is what we use for all our barrier qualification work.
The achieved WVTR of 0.72 g/m²/day gave a 28% headroom against the limit. That headroom became important later.
What Went Wrong on Run Three — and Why #
The first two production runs came back clean. Barrier test passed, graphics registered within our ±0.3mm tolerance on the label wrap print, end cap fitment torque was in spec. The brand approved the samples and we scheduled a 15,000-unit pilot production.
Run three, at production speed rather than sampling speed, produced delamination between the outer kraft body ply and the middle PE laminate layer. Not catastrophic — no open seams — but visible as a soft blistering under the label wrap on approximately 12% of tubes. Under our internal QC-14 body wall inspection protocol, anything above 3% delamination incidence is a hold-and-investigate event.
The root cause took us four days to isolate. Three factors combined:
First, the body paper moisture content had shifted. The spiral winding process is sensitive to paper moisture because the adhesive penetration rate into the ply surface changes. Our incoming material spec calls for kraft body paper at 6–8% moisture content per GB/T 462. The batch used in run three was at 9.3%, confirmed by our incoming lab. At that moisture level, the PVA-based winding adhesive was achieving only partial surface wet-out before the mandrel pressure was applied, leaving micro-voids at the laminate interface.
Second, the production floor humidity during that week had reached 78% RH — well above our controlled winding room spec of 55–65% RH. The winding room HVAC had been serviced two days prior and the set point had drifted. High ambient humidity compounded the paper moisture problem because the open-wound tube body was absorbing atmospheric moisture before the adhesive cured under the drying tunnel.
Third — and this is the factor that actually made the delamination visible rather than latent — the PE laminate extrusion temperature on that run had been dialled down by 8°C from our validated 320°C setpoint. The operator had made the adjustment to compensate for what he thought was an adhesive over-penetration issue from a different job earlier that shift. The lower extrusion temperature reduced the PE-to-kraft bond strength from our typical 3.8 N/mm (measured by ASTM D1876 T-peel) to approximately 2.1 N/mm — below our 2.5 N/mm minimum release threshold.
Any one of those three conditions alone would probably not have caused visible delamination. Together, they pushed past the failure threshold. The 15,000-unit pilot was put on hold. We sorted the lot, scrapped approximately 1,800 units (12%), and rebuilt the production with corrected parameters.
The corrective action that actually stuck: we added real-time paper moisture logging at the winding station entry, tied to our batch record system. If incoming moisture reads above 8.5% on the in-line sensor, the line stops automatically. That change cost us roughly three working days to implement. We have not had a recurrence across six subsequent production runs totalling approximately 95,000 units.
Does the Composite Can Actually Deliver the Shelf Life the Metal Tin Did? #
For this product category, yes — with the right liner specification. The foil inner liner in this build is 9 µm aluminium laminate, which is the spec we’d use for any nut or roasted snack with a water activity above 0.4. For lower-sensitivity products like tea or powder supplements, we sometimes step down to a 12 µm metallised PET liner, which reduces cost but raises WVTR to approximately 1.4 g/m²/day. That would not have met this brief.
The 0.72 g/m²/day result, with 28% WVTR headroom against the <1.0 g/m²/day target, gives the brand roughly equivalent real-world shelf performance to the tinplate at ambient retail conditions. The key variable is retail environment — the model holds for European and Australian retail. For Southeast Asian humid climates, we’d want to revisit the liner spec.
Specification Notes for Brand Partners #
When you brief us on a metal-to-composite conversion project, the most useful starting information is: your current pack dimensions, the barrier performance your existing pack achieves (or the shelf-life claim you need to support), and your annual volume. Volume matters because the choice between spiral-wound and convolute construction, and the liner specification, both have cost-per-unit profiles that shift at around 50,000 units annually.
The brief gap that causes the most sample iterations is incomplete product data. We need water activity or WVTR requirement, not just “12 months ambient shelf life.” Without a barrier target number, we’re guessing at the liner spec, and that typically costs two to three sample iterations.
Our standard sampling timeline for a composite can conversion is 18–22 working days to first physical samples, assuming confirmed dimensions and barrier spec. What extends that timeline is late changes to cap fitment style (metal vs. paper vs. plastic end cap), which affects the mandrel tooling. If you’re deciding between end cap materials, flag that at brief stage rather than after tooling is cut — tooling adjustments add 7–10 working days.
FSC chain-of-custody certification applies to our kraft body papers across all standard grades, which matters if your brand has sustainability commitments on fibre sourcing.
Frequently Asked Questions #
What caused the 12% delamination rate in run three, and how was it prevented from happening again?
Three conditions converged: incoming paper moisture at 9.3% (above our 6–8% spec), ambient winding room humidity at 78% RH after an HVAC fault, and a PE extrusion temperature 8°C below our 320°C validated setpoint. Any one factor alone would likely have been manageable. The permanent fix was automated in-line moisture sensing at the winding station entry, with a hard stop above 8.5% — confirmed effective across approximately 95,000 units since implementation.
Is a 0.72 g/m²/day WVTR result good enough for a nut snack with a 12-month ambient shelf life claim?
It depends on the water activity of the product and the worst-case retail humidity in your target market. For European and Australian retail, with a product water activity below 0.5, yes — 0.72 g/m²/day against a 1.0 g/m²/day limit gives meaningful headroom. For consistently humid retail environments above 80% RH, we’d revisit the foil liner gauge or consider a heavier laminate construction.
How does the 27-working-day production lead time compare to the metal tin it replaced?
The metal tin was running at 35 working days from the same supplier base, so the composite can came in 8 working days faster. The practical reason is that composite tube winding is a continuous-run process; tinplate fabrication involves more tooling change steps at volume.
Can the same composite can body be printed directly rather than using a label wrap?
Direct offset litho on the outer kraft ply is possible and gives cleaner registration than label wrap on textured surfaces, but it requires a coated outer ply rather than natural kraft. For this project the brand specified a tactile uncoated finish, which made label wrap the only print route. The registration tolerance we hold on our label wrap line is ±0.3mm, which was adequate for the design — no fine-line elements near the seam.
Planning a packaging project? Contact our team to request a complimentary specification review and sample quote.
The 8/10 drop pass rate at 1.2m would have stopped us cold — our retailer spec (Tesco ambient snack range) requires 10/10 at that height, no exceptions. We actually had a composite can body wall validated at 1.85mm that kept delaminating at the bottom curl during transit simulation, and it took us three supplier iterations to figure out the foil inner liner adhesion was degrading under the crimping pressure used for the metal end.
The 8/10 drop pass rate would’ve flagged as a rejection in our qualification protocol — we hold composite cans to 10/10 at 1.2m for anything going into e-commerce secondary packaging. Curious whether the two failures were base-seam or body wall.
The index 69 landed cost is solid for 180k units annually, but what doesn’t show up in that table is the tooling amortisation on the composite can mandrel and winding tooling — we paid around £4,200 for a custom diameter at a similar volume, which effectively eroded the first year’s savings by about 40% before we broke even on the conversion.
The 0.72 g/m²/day WVTR is interesting but we’d want to see that retested after 6 weeks of ambient ageing on the formed can — we ran the same ASTM E96 Method B protocol on a 3-ply composite body for a coffee SKU last year and saw barrier creep from 0.61 up to 0.89 g/m²/day after 42 days, which pushed us outside spec on a <0.85 target.
The foil inner liner is the part that keeps tripping us up on recyclability claims — we’ve had composite cans rejected from our retailer’s “widely recyclable” on-pack scheme twice now because the foil layer can’t be separated cleanly at kerbside, even when the body wall itself is 90%+ paper fibre by weight. We’re currently trialling a metallised paper barrier as a foil substitute on a 70g candle lid component, but getting the WVTR down anywhere near 0.72 without the foil layer has been the sticking point since Q1 this year.
The wall delamination issue they mentioned on run three — we had almost the exact inverse problem, where it didn’t show up until the cans were in secondary shipping cases. 72-hour transit simulation was clean, but a 3PL holding delay of about 11 days in a non-climate-controlled facility in the West Midlands caused the outer paper wrap to separate from the PE interlayer across roughly 30% of the affected pallet. Our converter traced it back to insufficient corona treatment on the PE film prior to lamination — dyne level had dropped to around 34 mN/m against a 42 mN/m spec. Ended up being 14,400 units quarantined.
One thing worth flagging on that 25 µm LDPE laminate spec — we found that nominal gauge from the converter and actual caliper after winding can drift enough to affect seal integrity, so we added a incoming goods check against ISO 4593 on every reel before it hits the line.
Was the <1.0 g/m²/day WVTR target modelled specifically against the nut oil migration interaction with the LDPE layer, or was it purely a moisture ingress calculation — because we've seen lipid content in high-oleic snacks accelerate PE swell enough to shift effective barrier performance outside the modelled shelf life window around month 9?
The 1.82mm body wall caliper works fine in isolation, but we couldn’t get consistent curl formation on the composite end once we pushed past 1.80mm — the fibre layers were resisting the metal end curl tool enough that we were seeing micro-tears at the seam junction on roughly 1 in 40 units at our Northampton line. Took us three tool geometry adjustments and about six weeks to dial in a revised curl radius that accommodated the stiffer body wall without compromising the hermetic seal.
The 27-working-day lead time matches almost exactly what we were quoted by our Shenzhen supplier on a similar conversion, but what actually ate into that window was first-article inspection sign-off on the spiral-wound body seam — they were using a different adhesive grade than what was documented in the pre-production sample, and we didn’t catch it until the FAI caliper check flagged inconsistent wall build at the overlap zone. Added 6 days to the cycle just getting the corrected material cert and a re-run of 50 pilot units shipped for our approval.