Lack of verification. Sometimes people will dump a material into another cotainer based on the color or appearance of the pellets without verifying that the materials are the same. This can also be an issue if someone switches over a feed line without verifying that the correct material is being sent to the correct location. It is therefore critical to clearly label all materials including regrind. Make sure that anyone that handles material understands the importance of getting the correct material into the correct containers. Also make sure that everyone who grinds runners or parts understands the correct grinder to use. Also when a silo is to be loaded make sure that someone has verified that the tanker is hooking up to the correct silo (this can be set up with different fittings as a poka-yoke).