Molded Pulp Wall Thickness Control: Where It Matters and Where It Does Not

Thick-wall molded pulp can hold 2–4 mm of wall, but thickness concentrates at corners and thins across flat spans. Understanding this flow behavior prevents both over-design and under-design.

The Scenario: A tray that warped at the warehouse

A logistics company ordered thick-wall trays for reusable parts bins. The trays warped within three months, and inspections showed walls varying from 1.2 mm at flat centers to 3.8 mm at corners.

Pain Points

• Flat spans dried thinner than spec, weakening the load deck;
• Corner thickness created uneven drying, driving warp;
• QA measured only average thickness, missing the distribution.

The Solution: Designing for the flow, not the average

The redesign added ribs under flat spans and moved material into the load path instead of chasing uniform thickness:

1. Ribbed flat spans Ribs stiffen thin areas, so the deck carries load without needing uniform wall.

2. Corner radius tuning Larger corner radii reduce material concentration and drying stress.

3. Thickness mapping in QA QA now maps thickness at defined points per TAPPI T 411 methods.

The Result: Warp gone, spec realistic

The revised tray held flatness through six months of use. The engineering spec now states minimum wall at load points instead of an average, which the molder can actually hold.