Whitening that appears only as the part leaves the tool is a release defect. The polymer is being bent, stretched, or scraped beyond its stable strain at the demolding temperature.
The likely causes are insufficient stiffness, undercuts, low draft, shrinkage onto a positive tool, rough surfaces, or excessive air-eject and stripping force. Uneven cooling can leave one region soft while the rest of the part releases normally.
Corrective action
The exact moment and location of whitening should be observed. Cooling should be increased only if the affected area is still too soft. Draft, undercut, surface finish, tool temperature, and release direction must be checked at the same time.
More eject pressure is not a safe first response. It can turn whitening into tearing or permanent distortion. The part should release with controlled deformation that remains within the material’s recovery capability.