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        # Troubleshooting Fish-Eyes in PVC Extrusion

        

**Topic:** Technical

        

Your extruded film or sheet looks like it has 'measles'. Small, un-melted clear spots are ruining the surface finish and transparency.

        
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## Problem

'Fish-eyes' are essentially high-molecular-weight resin particles that failed to fuse with the rest of the melt. This can be caused by poor resin quality, contaminated recycled material, or an inefficient mixing process.

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## Likely cause

This issue often stems from inconsistent compounding temperatures, inferior raw material purity, or unbalanced stabilizer ratios within the formulation matrix.

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## Corrective direction

The first step is to ensure you are using a high-quality NBT Resin with a narrow particle size distribution. Secondly, check your lubricant balance; too much external lubricant (like Stearic Acid) can prevent the friction needed for proper fusion. Finally, ensure your screen pack is clean and of the correct mesh size.

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          ## Frequently Asked Questions

          
### Does moisture cause fish-eyes?

Moisture usually causes bubbles or streaks; fish-eyes are almost always a fusion or contamination issue.

### Can I just increase the temperature?

Increasing heat might help, but it risks degrading the rest of the compound. Better to fix the formulation or mixing.

        
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By NBT Technical Desk · Updated 2026-06-07

        

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