What is flash in two shot injection molding? Description 2nd material penetrating between 1st material and its cavity. It is observed frequently where 1st material shrinkage is big and cooling time for 1 material is too long. It is mainly due to too fast shrinking of 1st material. How to trouble shoot the flash? 1.Optimizing holding pressure & Cooling time to get min shrinking of 1st material till before 2nd shot molding. 2.Select less shrinkage rate material for 1st shot. 3.Changing design as preventive action. We’ve spent the past 15 years accumulating rich practical experience in solving the flash of two-shot injection molding. HS Mold has the design, engineering, and in-house tooling capabilities you need to streamline your project 2k injection molding project from conception to production.