5 Common Problems in PVC Foam Extrusion and How to Fix Them

In our previous post, we discussed how to use extrusion moulds correctly to produce high-quality PVC foam boards and profiles. But even with the best mould design and advanced extrusion equipment, things don’t always go as planned.

If you’ve ever dealt with surface defects, uneven foaming, or unstable extrusion speed — you know the frustration. Don’t worry though — most of these issues can be solved with the right adjustments and understanding of how PVC foam moulds actually work.

Let’s look at five common extrusion problems and how to fix them like a pro.

1. Uneven Foaming or Density Differences

The problem:
Sometimes, you’ll notice that one part of the PVC foam board feels denser than another, or the foaming isn’t uniform.

The cause:
This often happens when temperature control or raw material mixing isn’t properly balanced. If the extrusion temperature varies across different zones, the foaming agent may react unevenly.

The fix:
Check the extrusion temperature profile — keep it consistent from the feed zone to the die head. Also, ensure your foaming agent and PVC resin are mixed evenly before feeding.
As we mentioned in the previous article, material quality and precision are everything. Small inconsistencies at the start often lead to big defects at the end.

2. Rough or Matt Surface on the Board

The problem:
The final PVC foam board looks rough or lacks gloss — definitely not ideal for furniture or decorative use.

The cause:
Usually, this is due to contamination or wear inside the extrusion mould, or sometimes a low extrusion temperature that prevents full melt formation.

The fix:
Clean the die lips and flow channels regularly and inspect for scratches. You might also need to slightly raise the die temperature or reduce the extrusion speed for better surface smoothness.
Remember what we talked about before? Regular maintenance is key to keeping your mould “young” and productive.

3. Warping or Bending After Cooling

The problem:
After the extrusion board cools, it starts to bend or twist.

The cause:
Uneven cooling or internal stress during foaming is the usual suspect. Sometimes, improper mould alignment can also cause tension differences across the product width.

The fix:
Adjust the cooling water temperature and make sure the mould outlet pressure is balanced.
If the mould itself isn’t aligned correctly, take time to recalibrate it — it might feel like a small thing, but it’s one of those “little details that change everything.”

4. Yellowing or Burn Marks

The problem:
PVC foam boards show yellowish or dark streaks — not only ugly but also a sign of chemical degradation.

The cause:
Overheating or staying too long in the barrel causes PVC to decompose.

The fix:
Lower the temperature slightly in the compression and metering zones, and check the stabilizer level in your formula.
And yeah, sometimes it’s not your mould — it’s the raw material formula that needs a tune-up.

5. Uneven Thickness or Poor Shape Stability

The problem:
The foam board comes out thicker in the center and thinner at the edges, or its edges start to curl.

The cause:
This usually means the die lip gap isn’t evenly adjusted, or there’s unstable pressure in the extruder.

The fix:
Inspect and re-balance the mould lip clearance and fine-tune the extruder output. Also, make sure your haul-off speed matches the extrusion speed — it’s like keeping your car engine and tires moving in sync.
Once the parameters are balanced, your PVC foam board will maintain perfect shape and thickness.

Producing flawless PVC foam boards is all about understanding the relationship between mould precision, material behavior, and process control.

As we explored in the previous article, good extrusion mould design and proper maintenance lay the foundation — but knowing how to troubleshoot common problems is what separates professionals from beginners.

At Hubei Junhui Mould Co., Ltd., our engineering team not only manufactures precision extrusion moulds but also provides customers with full technical support — ensuring that every mould delivers consistent, high-quality output throughout its lifespan.