PA 12 is used for functional parts that require high fatigue strength. This is mainly because it has better mechanical properties than ABS, and has excellent resistance to chemicals and abrasion.
Markforged, a manufacturer of 3D printing systems based in Massachusetts, has its own thermoplastic nylon called Onyx. It is a thermoplastic filled with chopped carbon fiber that is very stiff and can produce durable prints. Its micro-carbon reinforcement makes it twice as strong as ABS.
PA 6 is an excellent material for additive manufactured tools, prototypes, and production parts. It is has exceptional qualities because it is altogether strong and tough just like the Nylon 6, and is durable and dependable like FDM.