150, 300 or 500 gsm: Matching Pad Grammage to the Load Under It

Three pad grades on a supplier list, all the same size, all described as absorbent, differing only by a number most buyers ignore: 150, 300 and 500 grams per square metre. The price difference between the lightest and the heaviest is roughly 2.4 times. The capacity difference, measured under a 20 kg product load rather than in a beaker, is closer to 5 times. Grammage is the single most predictive specification on a pad and the one most often chosen by price.

This is a working guide to matching grammage to the load, with the numbers that convert a drip estimate into a grade, and the three situations where a heavier pad is the wrong answer.

What Grammage Actually Buys You

Grammage is the total mass of the pad per square metre, including carrier tissue and film. For a three-layer pad, the SAP core is typically 30 to 45 percent of that mass. So a 400 gsm pad carries about 140 to 180 grams of polymer per square metre, and at a working capacity of 12 to 18 millilitres per gram under load, that is 1.7 to 3.2 litres per square metre.

A 540 by 340 mm pad is 0.184 square metres. At 400 gsm it therefore holds 310 to 590 millilitres under load. As a rough planning rule across grades: 150 gsm gives 120 to 220 millilitres per pad, 300 gsm gives 240 to 440, and 500 gsm gives 400 to 730. Those are working figures, not saturation figures, and the gap between them is why a pad rated at 20 times its weight in a lab test disappoints on a tray.

The Load Table by Product

Multiply the tray weight by the drip percentage, then add 20 percent for margin and runoff. These are the resulting grades for a standard 540 by 340 mm pad.

• Whole muscle beef or lamb, 20 kg at 1.5 percent: 300 millilitres, needs 300 gsm.
• Pork shoulder, 20 kg at 3.5 percent: 700 millilitres, needs 500 gsm or two 300 gsm changes.
• Water-chilled chicken, 15 kg at 5 percent: 750 millilitres, needs 500 gsm.
• Whitefish fillets, 12 kg at 8 percent: 960 millilitres, exceeds one pad, needs a heavier cut or a mid-cycle change.
• Retail 400 g pack at 3 percent: 12 millilitres, needs 150 gsm.

The fillet line is the case that breaks the table, and it is why fillet operations run two changes rather than one very heavy pad. Beyond 500 gsm the pad becomes thick enough to lift the product off the tray base and to interfere with stacking.

Why Heavier Is Not Always Better

Three situations argue against the top grade. First, shallow trays: a 500 gsm pad swells to 10 to 12 mm when loaded, and in a 20 mm lip that leaves no room for the product without contact with the tray above. Second, retail packs, where a thick pad is visible through the film and reads to shoppers as padding. Third, short thaws under four hours, where the pad never approaches capacity and the extra polymer is simply cost.

There is also a rewet consideration. A heavily loaded pad under a heavy product can express liquid back into the meat when the stack is compressed, which is worse than a saturated thin pad in an open tray. Working capacity under load, not free swell, is the specification that predicts this.

What to Put in the Purchase Specification

Ask for grammage with a tolerance, typically plus or minus 5 percent, and for capacity measured under a stated load. A pad specified as 400 gsm with 450 millilitres retained under 20 kg for 24 hours is a usable specification. One specified as highly absorbent is not.

Then verify. Weigh ten pads from a delivery on a 0.01 g scale, divide by the cut area, and compare with the label. A 540 by 340 mm pad at 400 gsm should weigh 73.6 grams. Suppliers who are 8 percent light are not necessarily cheating, but they are selling you a different grade.

Grammage is the cheapest lever on pad performance and the easiest to audit at goods-in. Our SAP pad cores graded from 150 to 500 gsm are quoted with load-tested retained capacity, not free swell.