Molded Pulp Cushioning Design: The Engineering Behind the Soft Landing

Cushioning in molded pulp is engineered, not incidental. Wall curvature, rib spacing, and clearance ratios convert impact energy into controlled deformation, following the same physics as foam cushion curves.

The Scenario: Replacing foam with geometry

An electronics OEM wanted to replace EPS foam with molded pulp for a 2 kg power supply. Early pulp prototypes transferred shock directly to the product, and drop tests failed at 76 cm.

Pain Points

• Flat pulp walls had no deformation stroke, so impact passed straight through;
• Pocket clearances were too tight, coupling the product to the tray;
• There was no cushion curve data for the pulp grade.

The Solution: Designing the deformation stroke

The redesign followed standard cushion-design steps: measure the pulp cushion curve, set drop height, then shape geometry to stay inside the allowable deceleration window:

1. Cushion curve testing Drop-test samples of the exact pulp grade to map deceleration vs static stress, per ASTM D1596 methods.

2. Rib-and-corrugation stroke Deep ribs and curved walls add a controlled crush zone that absorbs impact energy.

3. Clearance ratio tuning Pocket clearance of 5–8% of product dimension lets the tray flex without coupling.

The Result: Passing at 122 cm

The redesigned tray passed the OEM's 122 cm drop requirement with peak deceleration 23% under the product limit. The foam was replaced across three SKUs.