Cooling & trim defect
Chill marks in thermoforming
Also called: Chill lines, mark-off
Chill marks (or mark-off) are visible lines or blemishes left where the hot sheet contacted a colder object — a plug, the tool edge or a frame — before forming completed, freezing a mark into the surface.
Why it happens
- Plug assist too cold relative to the sheet
- Premature contact with tool or frame edges
- Tool running below the ideal temperature
- Slow forming letting contact points cool
How to fix & prevent it
- Heat/temperature-control the plug assist (syntactic foam)
- Time the forming so contact is brief and even
- Hold the tool at the correct temperature
- Use felt or heated plug materials for show faces
How Indu prevents it: We use temperature-managed syntactic-foam plug assists and hold tools at the right temperature so plug and edge contact does not mark the visible surface.
Troubleshooting help
Fighting chill marks on a part?
Send your drawing, sample or a photo of the issue — our engineers will diagnose the cause and reply with the tooling, material and process fix, usually within 24 hours.
ISO 9001:2015 certified · Most quotes back within 24 hours