The term "flow mark" is used to describe the phenomenon where a striped pattern is formed around the gates when plastic has flowed through the die.

In this, plastic which has been cooled by sprues and runners is further cooled in the cavity and filling occurs at high viscosity. Consequently, plastic in contact with the mold surface is pressurized in a semi-solidified condition and stripes perpendicular to the flow direction are formed on the surface of the molded product.