TL;DR: How you store and transport packaging materials between LCA stages matters more than most specification sheets acknowledge — poor conditions invalidate emission baseline data.
TL;DR: Moisture absorption above 8% by weight in recycled fibreboard can shift cradle-to-gate carbon calculations by 4–7% when dry-weight mass assumptions are used in the LCA inventory.
How Storage Conditions Corrupt LCA Inventory Data Before a Product Ships #
Packaging LCA models are only as accurate as the physical inputs they’re built on. When we run cradle-to-gate assessments for brand partners, one of the first questions we ask is: where is this material stored, and under what conditions? The answer changes the numbers more often than people expect.
Recycled content paperboard and moulded pulp — two materials increasingly favoured for their lower embodied carbon — are hygroscopic. At 70% relative humidity (RH) and above, virgin kraft liner gains moisture at roughly 0.4–0.8% per hour during the first 6 hours of exposure in an unconditioned warehouse. Recycled-content board with OCC (old corrugated containers) furnish can reach equilibrium moisture content (EMC) of 10–12% in those same conditions, compared with a nominal specification of 6–8% per ISO 287 moisture testing. If your LCA practitioner used dry-weight density assumptions from a supplier data sheet measured at 23°C / 50% RH, the real-world mass of the material entering your production run is measurably higher. That means transport emission factors applied per tonne-kilometre are understated.
The table below shows how storage environment affects key physical parameters used as LCA inventory inputs for three common packaging substrates:
| Substrate | Nominal GSM (ISO 536) | EMC at 50% RH | EMC at 75% RH | Mass error in LCA at 75% RH |
|---|---|---|---|---|
| Recycled-content SBB (350 gsm) | 350 g/m² | 6.8% | 10.4% | +3.5% per tonne shipped |
| Virgin kraft liner (200 gsm) | 200 g/m² | 6.1% | 9.2% | +3.1% per tonne shipped |
| Moulded fibre tray (700 µm wall) | ~450 g/m² eq. | 7.5% | 12.1% | +4.6% per tonne shipped |
These are not worst-case figures. They are representative of typical coastal-warehouse conditions in Guangdong in July and August, when outdoor RH regularly sits at 80–90% and temperature-controlled storage is inconsistent.
The decision-making implication is direct: if your LCA report was commissioned using supplier-declared weights and you are storing materials in unconditioned space, that report has a systematic error baked in before you’ve run a single machine. For brands publishing carbon footprint claims against PAS 2060:2014 or applying for Environmental Product Declarations (EPDs) under ISO 14025, this is a documentation gap that third-party verifiers will flag.
What Goes Wrong When Packaging and LCA Data Are Managed in Silos #
There are three failure scenarios we see repeatedly when brand partners bring us into a project mid-stream — after the LCA has already been filed but before production has started.
The first scenario is substrate substitution without LCA update. A brand approves a 350 gsm recycled SBB for their outer carton based on an LCA that used primary data from their nominated mill. During a supply disruption, the procurement team approves an alternate 370 gsm board from a different mill with a higher OCC fraction and different process energy intensity. The structural engineer signs off because the stiffness is equivalent. The LCA is not updated. We caught one of these in early 2024, flagged under our MR-04 material replacement review procedure, when a carton line changeover was documented and the incoming lot weight was 5.8% above the LCA-registered value. The EPD the brand was using for retailer compliance was based on the original substrate. Two sample iterations and a partial LCA revision followed.
The second scenario is temperature excursion degrading coating integrity. UV-cured or aqueous coatings on folding cartons are specified partly for their barrier performance, which feeds into recyclability credits in end-of-life LCA modules. If finished cartons are stored above 40°C for more than 48 hours — common in unventilated container holds on summer sea freight — aqueous coatings can delaminate at the micro level. Visually the carton looks fine. But the barrier reduction affects oxygen transmission rate (OTR), and if the LCA included a functional unit assumption about product protection extending shelf life, that assumption no longer holds. The carbon amortisation over product uses is then overstated.
The third scenario is transit packaging damage inflating secondary emission intensity. When folding cartons are shipped in corrugated master cases and those cases are crushed beyond the ECT (edge crush test) threshold — typically 30–50 kgf/cm for a standard B-flute RSC — printed cartons inside suffer crease distortion that generates scrap at the filler line. We’ve tracked fill-line rejection rates of 3–6% on jobs where transit packaging was underspecified relative to palletisation stack height. That scrap rate translates directly to wasted upstream manufacturing emissions: the carbon cost of producing those rejected units is real and should theoretically appear in your Scope 3 waste disposal emissions. It rarely does, because the connection between transit spec and LCA boundary is not drawn in most briefs.
What to check in each case: verify substrate lot numbers against the LCA inventory, log any approved substitutions under a change control process, confirm storage temperature records for finished goods before they are loaded, and specify transit packaging to ISTA 2A or equivalent for any sea freight lane longer than 14 days.
Does Warehouse RH Actually Affect the Carbon Number on a Label? #
Yes, but only when the LCA uses actual transported mass rather than theoretical dry weight — and that distinction depends on which system boundary and functional unit the practitioner selected.
For brands declaring a per-unit carbon figure on-pack, the transport module (typically A4 in a cradle-to-gate-with-options scope) is calculated per tonne-kilometre multiplied by declared weight. If 10,000 carton blanks are declared at 28 kg per thousand and are actually running at 30.2 kg per thousand after warehouse moisture uptake, the A4 transport emission is understated by roughly 7.9% for that module. This is a small number in isolation. Across a full product range with 40+ SKUs and a mix of sea and air freight, the aggregate distortion can be meaningful enough to affect a Scope 3 Category 1 (purchased goods) inventory. The boundary matters. For most short shelf-life product packaging shipped by sea in containers with nominal temperature control (18–24°C, 55–65% RH target per most freight contracts), the effect is manageable. For high-surface-area moulded pulp shipped in bulk in humid summer months, we’d recommend weighing incoming lots at goods receipt rather than relying on supplier-declared weight.
Specification Notes for Brand Partners #
When you brief us on packaging for a product where an LCA is in scope, the most useful thing you can send alongside your structural brief is the system boundary and functional unit your LCA practitioner has defined. That single document tells us whether substrate weight, transport distance, or end-of-life scenario is the most sensitive variable for your carbon figure — and we can then specify materials and transit packaging accordingly.
The brief gap that causes the most avoidable rework: brands specify the primary packaging substrate correctly but leave transit packaging (master case spec, palletisation pattern, layer count) undefined. Because transit packaging contributes to both the Scope 3 upstream inventory and the functional protection assumption, leaving it open means the LCA practitioner and the structural engineer are working from different assumptions. We ask for a confirmed pallet pattern and warehouse stack height before we finalise master case specification.
Our standard material data collection for LCA support takes 5–8 working days for primary substrates where we have existing supplier Environmental Product Declarations on file. For new substrates or custom laminates, allow 15–20 working days to gather primary data. Sampling lead time for the packaging itself runs on our normal schedule: 12–15 working days for folding cartons, 20–25 working days for rigid boxes.
Frequently Asked Questions #
If my LCA was completed six months ago and I’ve since changed warehouse locations, do I need to redo it?
It depends on whether the new warehouse meaningfully changes your transport emission assumptions or your storage condition assumptions that feed into material mass data. If the new location is more than 200 km from the original point of use declared in the A4 transport module, and you are working toward a verified EPD or PAS 2060 declaration, a practitioner review is warranted — not necessarily a full redo, but at minimum a sensitivity check on the transport and storage modules.
What RH level should our packaging warehouse maintain to keep LCA mass assumptions valid?
The ISO 187 conditioning standard specifies 50% RH ± 2% and 23°C ± 1°C for paper and board reference conditions. Holding your warehouse to exactly those numbers is unrealistic for most commercial operations, but staying below 65% RH and below 30°C will keep moisture uptake within the 1–2% range for most substrates — small enough that the mass error in LCA transport calculations stays under 1%, which is below most EPD programme operator rounding thresholds.
Can we credit reduced transport emissions in our LCA if we switch from corrugated master cases to tighter-nested flat-pack shipper trays?
Yes — this is a legitimate system design change that reduces transport volume per unit and therefore tonne-kilometre impact. The credit is real but often smaller than brands expect: a 15–20% reduction in shipper volume typically translates to a 3–5% reduction in the A4 transport module, which is usually a minor contributor to total cradle-to-gate carbon anyway. The bigger gain from flat-pack consolidation is usually in reduced transit damage rate, which cuts manufacturing scrap and the associated upstream emissions.
How do we handle a situation where our fill-line scrap rate is higher than the 2% default some LCA tools assume?
State your actual scrap rate as primary data and override the default. Most LCA software tools allow you to enter a process yield figure — if your fill line is running 4.5% rejection on a carton format, enter that rather than accepting a generic industry default. The difference between 2% and 4.5% process waste adds measurable upstream manufacturing emissions to your product’s carbon footprint, and understating it is a data quality issue that third-party reviewers will challenge under ISO 14044 data quality requirements.
Planning a packaging project? Contact our team to request a complimentary specification review and sample quote.
