Sealing Types and Leakage Risks in Compostable Liners
Table of Contents
Why Sealing Matters for Leakage
Many compostable liners leak not because of thickness, but because of how the bag is sealed.
The sealing type controls:
- Where stress builds up
- How weight and liquid are distributed
- How likely the bag is to leak or split
This page explains the main sealing types used in compostable liners, how each affects leakage risk, and how to choose the right option for real-world use.
What Is a Bag Seal?
A bag seal is the area where the film is joined together to close the bottom or sides of the liner.
In compostable liners, the seal must:
Hold liquid and weight
Stay intact under movement
Perform consistently across batches
Most leakage problems start at the seal, not the film itself.
Common Sealing Types Used in Compostable Liners
Flat Bottom Seal
Flat bottom seals close the bag with a straight seal across the base.
Advantages
Simple structure
Lower production cost
Leakage risks
Stress concentrates at the corners
Liquids pool directly on the seal
More likely to leak when overfilled
Flat seals are more sensitive to heavy or wet waste.
Star Seal (Star Bottom Seal)
Star seals gather the film into a star-shaped closure at the bottom.
Advantages
Weight is spread evenly
Bag conforms better to bin shape
Reduced stress at single points
Leakage risks
Depends heavily on seal quality
Poorly sealed stars can still leak
Star seals are widely used for wet waste and food scraps.
Side Seal (Side Weld Seal)
Side seals join the film along the sides of the bag.
Advantages
Simple structure
Common in small liners
Leakage risks
Side seams are exposed to movement
Liquids can travel along seams
Higher risk under swinging loads
Side seals are less forgiving for heavy or liquid waste.
Gusseted Seals
Gusseted bags include folded sides that expand with the load.
Advantages
Better bin fit
Improved volume capacity
Leakage risks
Folded corners create stress points
Seal quality must be very consistent
Gussets improve fit but do not automatically reduce leakage.
How Sealing Type Affects Leakage Risk
Leakage usually happens because of:
- Stress concentration at corners or seams
- Liquid pressure building at the bottom
- Uneven seal strength
- Movement inside the bin
Sealing types that distribute load evenly reduce these risks.
Leakage risk is often linked to thickness consistency as well.
See Thickness vs Performance in Compostable Trash Bags
Sealing Types Compared at a Glance
| Sealing Type | Leakage Risk | Typical Use |
|---|---|---|
| Flat Seal | Higher | Light or dry waste |
| Star Seal | Lower | Wet food waste, kitchen liners |
| Side Seal | Medium–High | Small or light liners |
| Gusseted | Medium | Better bin fit, moderate loads |
This table shows general trends.
Actual performance depends on seal quality and use conditions.
Sealing and Wet Food Waste
Wet food waste creates extra pressure at the bottom of the bag.
For compostable liners:
Liquids weaken material over time
Movement increases stress on seals
Poor seals leak even in thick bags
Star seals are often preferred for food waste, but quality still matters.
Learn more about wet waste performance in Are Compostable Bags Strong Enough for Wet Food Waste?
Why “Good Seal Design” Still Fails
Even the right sealing type can fail if:
Heat sealing is uneven
Seal width is inconsistent
Thin spots exist near the seal
Storage time is too long in hot conditions
This explains why two bags with the same seal type can perform very differently.
How Buyers Can Reduce Leakage Risk
Instead of choosing by name alone, buyers should:
- Test liners with water before bulk use
- Check seals for continuous, even lines
- Avoid overfilling bags
- Match seal type to waste type
Simple testing catches most leakage problems early.
What to Check When Sourcing Compostable Liners
For B2B buyers, sealing should be part of supplier evaluation.
Check:
- Seal consistency across samples
- Seal strength under load
- Batch-to-batch stability
- Performance with real waste
For a full evaluation framework, see How to assess a compostable bag manufacturer
Conclusion: Sealing Type Directly Affects Leakage Risk
Leakage is rarely caused by thickness alone.
In compostable liners, sealing type and seal quality play a major role in performance.
Understanding how different seals behave helps buyers choose liners that leak less, perform better, and reduce complaints.
