The work presented aims to investigate the filling process of a protective mask for design validation and ergonomics by creating a silicone replication in a 3D printed mold tool for small series of production. The object of analysis is a protective mask with UV-C protection technology, which should ensure the sterilization of bacteria and viruses in inhaled and exhaled air using UV-C light. Applying additive manufacturing FDM technology to create a complex three-part mold tool improves the process of design and ergonomic parts which can be referred to cost effective method for small series. By creating a silicone replica of the mask, an assessment of accuracy and precision is made to validate design and ergonomics before proceeding to final tooling design.