When printing on clear films, foils, colored, and metalized stocks, white ink is an additional color that can be used in the design, or as an element to help graphics stand out. NOTE: White ink is not necessary when printing on white paper or film.
In Illustrator, create a new layer above the art layer and call it “White“.
Open the Swatches window and create a new swatch. The build that we use is C=20, M=0, Y=0, K=0. Name the new swatch “White” and be sure to make it a spot color. In your White Layer, apply the new White Spot Color to all the elements that you want to print in White.
For metallic elements, just apply that same White Spot Color to it and change the tint to 0%. Also, be sure to set all the objects on your white layer to Overprint in the Attributes window.