C4D XL 6 has various primitives which it doesn't convert to polygons until render time From what I know, it's converting all of them right before it starts rendering, where REYES renderers like PRMan create their micropolygons only for the current bucket (Buckets are those patches you see when FireFly is rendering. That's why a lower bucket size makes FireFly require less RAM.). cylinders which are mathematical representations of cylinders only (until render time or conversion to polys) Actually, these are never ever being converted into polygons. Mathematical primitives that can be expressed as a formula like cylinders or spheres are easier to render as perfect spheres than as polygons.