Why Do Courier Bags Keep Opening? 3 Common Sealing Mistakes!

2026.07.14

Site Editor:

A courier bag may look simple, but one weak seal can lead to damaged products, customer complaints, and expensive returns.

Many manufacturers assume the problem is caused by poor raw materials. In reality, sealing failures often result from incorrect machine settings, worn sealing components, or unstable production conditions.

If your courier bags frequently split open during transportation, this guide explains the three most common sealing mistakes and how to fix them before they affect your production line.

Why Seal Strength Matters

Courier bags face compression, drops, stretching, friction, and temperature changes. Reliable seals protect products throughout transportation.

Mistake 1: Incorrect Sealing Temperature

Low temperature creates weak bonds; excessive temperature burns or deforms the film. Adjust settings according to material type.

Mistake 2: Worn Sealing Knife

Carbon buildup, plastic residue, and worn edges reduce sealing consistency. Clean and replace sealing knives regularly.

Mistake 3: Uneven Film Thickness

Inconsistent blown film thickness produces inconsistent seal strength. Stable blown film quality is essential.

Other Factors

Sealing pressure, machine speed, cooling performance, and raw material quality also influence seal quality.

Modern Machines

PLC control, servo feeding, automatic temperature control, precision sealing knives, and tension control improve production consistency.

Maintenance Tips

Inspect knives daily, monitor temperature sensors, check film thickness, and replace worn components on schedule.

Choosing the Right Courier Bag Making Machine

When purchasing a machine, don't focus only on production speed.

A reliable machine should provide:

Stable sealing quality
Accurate temperature control
Durable sealing components
Easy parameter adjustment
Low maintenance requirements
Long-term production stability

Higher productivity means little if sealing quality cannot be maintained.

Conclusion

Correct temperature, healthy sealing knives, and consistent film thickness are the keys to producing reliable courier bags.