Flex is a children's casual shoes, using 3D printing technology production. Through the use of intelligent algorithms, the sole is customized according to the developmental characteristics of the child's foot. Producing shoes does not require assembly of individual parts nor glue, which simplifies the manufacturing process and reduces waste. The openwork surface allows personalized design by inserting various materials and decorations. Flex provides excellent fit and high wearing comfort, especially considering the anatomy of the child's foot.