Two Centimetres of Overhang: The Tray Sizing Error That Wicks Drip Into the Stack

A pork plant in Denmark cut its pads from a 1,000 mm master roll to 620 by 420 mm for a 600 by 400 mm Euro tray, because the extra 20 mm on each side looked like good coverage. Six weeks later, the bottom tray of every stack had a wet rim and the pallet underneath was stained. Nothing was wrong with the pad. The overhang was acting as a wick, pulling liquid off the tray and down the outside wall of the stack into the tray below.

Pad sizing is treated as a cutting-room task when it is really a hydraulic one. Three measurements decide whether a pad works: the tray floor dimensions, the internal lip depth, and the thickness the pad reaches when loaded. This article works through all three with numbers you can apply at the bench.

The Three Measurements You Need Before Cutting

Start with the internal floor, not the external footprint. A nominal 600 by 400 mm tray typically has an internal floor of 570 by 370 mm at the base, rising to 600 by 400 at the rim because the walls are drafted. A pad cut to 600 by 400 will not lie flat; it will buckle at the corners and lift at the centre, which is where the product needs contact.

The second measurement is lip depth, usually 20 to 40 mm on a standard meat tray. The third is loaded thickness: a 3 mm dry pad with a 4 gram SAP core swells to 8 or 9 mm when saturated, and a laminated pad can reach 12 mm. Both swollen thicknesses must sit below the lip, or the pad lifts the product and the tray no longer stacks squarely.

What Overhang Actually Does to a Stack

Liquid travels along a continuous fibre path by capillary action, and a 20 mm overhang folded over the tray rim creates exactly that path. Once the pad edge is wet, water climbs the outside wall of the tray at roughly 5 to 10 mm an hour depending on viscosity, reaches the base of the tray above, and appears as a ring of moisture on the tray below within a single thaw cycle.

The visible result is blamed on the tray above leaking, which sends maintenance looking for cracks that do not exist. The real fix costs nothing: cut to the internal floor minus 5 mm on each side, and let 10 to 15 mm of bare tray perimeter carry the runoff instead of the pad edge.

The Coverage Ratio That Replaces Guesswork

Coverage is the pad area divided by the tray floor area, and 85 percent is the practical floor. Below that, product overhangs the pad and drip lands directly on plastic. Above 95 percent you gain almost nothing and start fighting the overhang problem.

• A 570 by 370 mm floor is 2,109 cm². A pad of 540 by 340 mm is 1,836 cm², which is 87 percent. That is the working cut.
• For a 530 by 325 mm GN 1/1 pan, a 500 by 300 mm pad gives 87 percent and leaves a usable margin.
• For a 20 kg bulk bin at 400 by 300 mm internal, a 380 by 280 mm pad is 89 percent and is the smallest cut that still catches corner runoff.

Notice that none of these cuts matches the nominal tray size. That is the point. Sizing off the label is how plants end up with pads that buckle, wick and waste 8 percent of every roll.

Cutting, Nesting and the Offcut You Paid For

A 1,000 mm roll cut to 540 mm wide yields one pad per row plus a 460 mm offcut. If the same roll is cut to 340 mm, it yields two pads per row with 320 mm left over, which is the difference between 12 percent waste and 4 percent. On 4,000 pads a week that is 40 kg of material a month, and it is the easiest saving in the whole pad budget.

Nesting matters too. Pads cut to fit a specific tray cannot be used on another size without trimming, so a plant running three tray types should standardise on two cuts and accept a small coverage penalty on the third rather than holding three stock lines and three sets of part-used rolls.

Sizing is the cheapest part of pad performance to get right and the most expensive to get wrong. Our SAP absorbent roll stock for tray pads is supplied in widths that map onto standard meat and fish tray formats, which removes most of the offcut problem before it starts.