Self-intersections

Check if the shoe self-intersects, when some faces cross other faces. Self intersection can result in printing defects which compromise the final quality of the product. 

When Rejected:

Avoid areas with high concentration of small faces, self intersections result from not clean CAD operations (booleans, joining surfaces, displacement maps). 

Voxelize workflows can be a solution in some cases, but compromises the original topology, and should only be used in the last case.

SELF-INTERSECTION TIPS:

Most watertight and self intersection issues are the result of poor boolean operations or not well connected edges between surfaces  (Nurbs & Mesh). 

Establishing a clean 3D modelling workflow plays a major role in preventing watertight and self-intersection issues. Parametric Wizard suggestion is:

SUBD(shape)> NURBS OR MESH(details)> REDUCE MESH(decimation)> STLS