Hi guys,
I’ve been working through a few ZBrush tutorials and I really don’t understand what exactly “Make Polymesh3D” does. When I import something from Maya into ZBrush I can already sculpt on it. What is the reason for making it a Polymesh 3D? I’ve already searched google but I can’t come up with a definitive answer.
A polymesh is any model made up of polygons rather than being tied to some form of mesh generator.
An imported model is by default a polymesh. You don’t need to turn it into one.
ZSpheres, DynaMesh and parametric objects are examples of mesh generators. They must be converted to a polymesh before you can begin sculpting their polygons. Otherwise, the polygon structure is still in flux and so any sculpting is potentially subject to being lost.
For example, if you’re working with a Sphere3D and you were to change one of the Initialize settings the polygon structure would totally change. You don’t want to be sculpting in such an environment! Using the Make PolyMesh 3D button “bakes” the model – breaking its connection to the Initialize settings and making it safe to sculpt.
You don’t always need to use the Make PolyMesh button. For example, if you’re working with ZSpheres you can use Make Adaptive or Make Unified to convert the model to a polymesh. Either way, the result is that the model is no longer linked to the ZSpheres and their settings which means that it’s now a polymesh model and ready to sculpt.
Thank you so much! This was a huge help! 
It makes perfect sense now