Why Your Filter Paper Tea Bags Keep Leaking – And How to Stop It

In the competitive world of tea packaging, nothing damages customer trust more than a leaking tea bag. If your filter paper tea bags are breaking or leaking—especially along the vertical seal—you’re not alone. Many tea manufacturers and co-packers face this issue, and it often leads to customer complaints, product returns, and a damaged brand image.

So, why do these tea bags keep failing? And what can you do to stop it?

Let’s break it down.

What Exactly Is the Problem?

• Tea powder leaks through the side seam (vertical seal)

• The bag appears crushed, wrinkled, or burnt

• The seal line is incomplete or misaligned

• Customers complain: “The tea bag opened inside my cup!”

These symptoms point to a problem during the vertical sealing process on a four-side seal tea bag—especially when using filter paper materials.

Top 5 Reasons Your Filter Paper Tea Bags Are Leaking

1. Sealing Temperature Is Too High or Too Low

• If it’s too hot, the filter paper burns, shrinks, or becomes brittle.

• If it’s too cold, the sealing layer won’t melt properly, causing a weak bond.

Solution:
Adjust vertical sealing temperature based on your paper's sealing layer (e.g., PLA or PE). Ideal temperature range: 130–160°C, depending on paper thickness and coating.

2. Uneven Sealing Pressure

If the vertical sealing jaws apply uneven or excessive pressure, one side of the tea bag may appear flattened or wrinkled, damaging the paper and leaving weak spots.

Solution:
Recalibrate your sealing jaws. Make sure pressure is evenly distributed and not too high, especially when using thinner or eco-friendly filter paper.

3. Filter Paper Tension Not Stable

When the paper is fed with poor tension, it may wrinkle or drift sideways before reaching the sealing jaws. This leads to seals over creases, or misaligned edges.

Solution:
Use constant tension control systems and maintain smooth film feeding. Adjust unwind tension carefully during machine setup.

4. Poor-Quality or Incompatible Filter Paper

Not all filter papers are created equal. Some are too thin, poorly coated, or not heat-sealable under standard machine conditions.

Solution:
Use high-quality food-grade filter paper with proper sealing properties. Always test with small batches before mass production.

5. Tea Powder Overload Near the Seal Line

If tea powder enters the sealing area, it can block heat transfer, creating weak or unsealed zones. The trapped tea may also get crushed or burnt.

Solution:
Ensure correct dosing. Maintain 3–5 mm clearance between tea fill level and the sealing zone. Use dust collection systems if necessary.

How to Prevent This Problem Long-Term

Final Thoughts

If your filter paper tea bags keep leaking, the issue is often not with the customer, but with how the tea bag was sealed. By diagnosing problems like heat settings, pressure balance, and material quality, you can solve the root cause—before it reaches your customer.

Need expert help on optimizing your tea bag packaging process? Our team specializes in four side seal tea bag machines, eco filter paper solutions, and custom sealing setup to help brands improve quality and consistency.