Export shipments: pads, polyliner and a 30-day lane

Thirty days door to door, a forty-foot reefer, and a carton that has to arrive looking like it left. That is the brief for a chilled export lane, and it is the one place where a pad can quietly ruin a consignment. Not by failing to absorb, but by absorbing and then holding the moisture exactly where you do not want it: against the carton, inside a polyliner, for four weeks.

Frozen export is a different job and mostly easier. Chilled export at minus one to zero is where the pad, the liner and the carton have to be designed together.

Chilled and frozen are different problems

A frozen carton at minus eighteen has no liquid water to manage. Any pad in there is dealing with condensation on thaw, which is a receiving problem, not a shipping one. A chilled carton is the opposite: the product is above its freezing point, drip is continuous, and the carton is a closed box that will hold humidity for a month.

So the two lanes need different answers. Frozen: a light sheet to catch the thaw at destination, nothing more. Chilled: a sheet sized to the total drip over the lane, plus a liner arrangement that lets moisture migrate away from the board.

The sizing question is where most lanes go wrong. A buyer takes the domestic specification, which assumes three to five days, and applies it to thirty days. Drip does not arrive evenly: most of it is released in the first seventy-two hours, then a slow trickle for the rest of the month. A pad that is 80 percent full at day four is not empty at day thirty, it is saturated and wicking back into the board.

The layer order inside a lined carton

Bottom to top: carton, pad, product, pad, polyliner folded over the top. The second pad is not for absorption, it is a vapour buffer. It takes up the condensation that forms on the underside of the liner when the reefer cycles, which stops it dripping back onto the meat.

Two details decide whether this works. The pad must be slightly smaller than the carton base, so it does not wick against the wall, and the liner must be folded rather than sealed, so the carton can breathe at the seams. A sealed liner turns the carton into a terrarium.

Stack height is the other variable. Four cartons high on a pallet is fine for frozen and marginal for chilled, because the bottom carton carries the drip of everything above it if a pad fails. Three high, with a divider board between layers, is the arrangement that survives a long lane in our experience.

The rejection that came from a sealed liner

A lamb shipment arrived with two pallets rejected. The cartons were stained through the base and the buyer photographed a dissolved corner. The pads were fine, the temperature log was clean, and the cause was a liner that had been taped shut at the top. Moisture had nowhere to go, the pad reached saturation by day nine, and the remaining three weeks of drip sat in the board.

The fix cost nothing: fold the liner, do not tape it, and add four vent holes at the top corners. The next shipment on the same lane arrived dry.

What to inspect at the loading dock

Four checks, two minutes per pallet:

• Pad size against carton base, with a 10 mm margin all round.
• Liner folded, not sealed, with vents open.
• Carton weight against the nominal, which catches a pad that was left out.
• One carton opened per pallet, photographed, and resealed with tape marked with the time.

Also check the pad grade against the lane length. A sheet specified for a seven-day domestic run will be at its limit by day ten on a thirty-day lane, and the last twenty days are the ones that decide the claim. Ask the supplier for absorption at 4 °C over time, not just total capacity, because the two numbers diverge on a long lane. The pad user guide has a worked example for a 30-day chilled lane.