Wet-Strength and Water-Resistant Molded Pulp: How Additives Keep Trays Rigid in Cold Chain and Rain

Paper fiber loses up to 90% of its dry strength when saturated, which is why ordinary molded pulp fails in condensation and rain. Wet-strength resins such as polyamide-epichlorohydrin (PAE) at 0.5–1.0% and water-repellent sizing chemistries preserve rigidity and shape in wet conditions while keeping the material largely repulpable and recyclable.

The Scenario: Water weakens ordinary pulp

Wet-strength packaging faces three challenges:

Pain Points

• Saturated fiber loses most of its strength, so trays buckle under stacking weight in humid or cold-chain conditions;
• Condensation from cold-chain shipping and outdoor rain soaks packaging through, degrading fit and protection;
• Water-repellent coatings must not block recyclability or repulpability at end of life.

The Solution: Three wet-strength molded pulp solutions

Molded pulp offers three solutions for wet conditions:

1. Wet-strength resin treatment PAE resin at 0.5–1.0% keeps trays rigid and load-bearing even when saturated, preserving stacking strength.

2. Water-repellent sizing Internal sizing and surface repellency slow water uptake, keeping trays dry in condensation and rain.

3. Recyclable, repulpable chemistry Treatments are chosen to remain repulpable, so the material still recycles in the paper stream.

The Result: Rigid trays in wet conditions

With these solutions, trays hold shape and load through cold chain and rain. Shippers cut product damage from collapsed cushioning in humid environments.