Laser marking is fundamentally different from ink printing, the traditional method of marking on plastics. Direct ink printing puts an image on the surface of the plastic which can be removed by abrasion or solvents, but laser marking can provide an indelible high-contrast mark in the material itself, with no direct contact with the plastic other than through the incident laser beam. This application note looks at pulsed fiber laser marking of plastics focusing on the four key types of mark: foaming, engraving, engraving with color change and color change only marking. It also explores laser marking of different types of plastic including ABS, polyethylene, polypropylene and polycarbonate, and why the pulsed fiber laser is the best tool for the job.