Surfboards have been manually made for many years, thus becoming unique pieces, but with numerous physical and ergonomic risks for the health of the operator (shaper). With the recent technological advance, surfboard manufacturing shifted towards CNC milling, improving quality and reproducibility, as well as reducing the risks to the health of the operator. However, even though most of the current surfboards are manufactured industrially, the use of rigorous surface metrology is scarce to control the surface finish of CNC-milled expanded polystyrene (EPS) blanks. The present study aimed to evaluate the surface finish of EPS blanks machined by a CNC milling machine with a diamond disc tool, designed for surfboard manufacturing. Four EPS blanks of different brands and densities were characterized, machined at two feed rates: (a) 10 m/min and (b) 5 m/min, and the quality of the surface finish was evaluated. Scanning electron microscopy as well as a confocal laser scanning microscope were used to evaluate the surface morphology. A range of topographical parameters was proposed and assessed. The structural characteristics of the EPS blanks demonstrated that the machined material is easily mouldable, not causing damage to the tool, thus requiring little maintenance for tool periodic replacement. The use of confocal microscopy proved to be efficient for the evaluation of the quality of the surface finish of EPS blanks and a set of topographical parameters was chosen. The higher density blanks showed better surface finish after machining at the feed rate of 5 m/min, while the lower density blank had a better surface finish when machined at the feed rate of 10 m/min. In particular the parameters Ssk and Sku could detect problems in the surface morphology resulting from machining EPS blanks.