Cooling & trim defect
Sink marks in thermoforming
Sink marks are shallow surface depressions that form where material cools and contracts unevenly — typically over a thicker section or where the sheet contacted a colder part of the tool.
Why it happens
- Uneven wall thickness with thick spots
- Localised cold areas on the mould
- Cooling too quickly before the surface stabilises
- Excessive pressure pulling the sheet into detail
How to fix & prevent it
- Even out wall thickness across the part
- Hold uniform tool temperature (temperature-controlled tooling)
- Slow and balance the cooling stage
- Adjust vacuum/pressure to avoid over-pulling
How Indu prevents it: Temperature-controlled tooling keeps the whole mould at one temperature, which — with even wall design — is how we keep converted show surfaces free of sink marks.
Troubleshooting help
Fighting sink 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