The minimum thickness can vary based on the material, machine, and process, but most processes require a minimum thickness of .025” to .030”. Softer materials will require a thickness of at least .040”. Smaller features, walls, and geometries can be built but are geometry or build orientation dependent. Keep in mind that most 3D printing processes require some finishing and small, thin features are more delicate and take a lot of care to survive printing, processing, and shipping.