Molded Pulp Stacking Strength FAQ
How much weight can molded pulp packaging support in a stack?
Stacking capacity depends on wall thickness, rib and corrugation geometry, fiber furnish, and density. Ribbed or profiled designs carry substantially more than flat panels of the same weight. Instead of a universal number, buyers specify a target compression load and verify it with a box compression test on the actual part.
What is a box compression test (BCT) for molded pulp?
A box compression test places the package under a steadily increasing vertical load until it deforms or collapses and records the peak force. Standards such as ISO 2233 define conditioning, test speed, and reporting so results are comparable between suppliers and designs. Some buyers also run ISTA-style distribution tests that include stacking after simulated transit.
What design factors increase molded pulp stacking strength?
The main levers are rib and corrugation geometry, wall thickness, fiber type and refining, and molded density. Continuous load-bearing walls and column-like profiles beat flat spans, and well-refined longer fibers build stronger interlocking. Geometry improvements usually cost less than simply adding wall thickness.
Why does moisture weaken molded pulp in stacks?
Molded pulp is a fiber material, and wet or humid fiber loses stiffness. A part that passes a dry-lab compression test can soften noticeably in transit at 60–80% relative humidity or under condensation. Moisture barrier coatings, pallet wrapping, and dry storage preserve strength in real supply chains.
What should a molded pulp stacking spec include?
A defensible spec has four parts: the target load (for example, surviving 60 kg vertical load for 24 hours), the conditioning protocol (temperature and humidity before and during the test), the test method (ISO 2233 or an agreed ISTA protocol), and acceptance criteria such as maximum allowable deformation at the target load.
How is compression strength reported by suppliers?
Reputable suppliers report peak load in kilograms or newtons, the conditioning used, the test standard, and the deformation curve. Ask for the conditioning details explicitly — a compression number tested at dry lab conditions will overstate performance in humid climates where the package actually stacks.