What's the difference between a closed polysurface and a closed extrusion?

Is the distinction just for record keeping purposes, or is there more than meets the eye?

When an object can be described by a curve and an extrusion length thereof (and potentially closed), you can reduce the size / memory consumption of the model which in turn gives better performance in large files. As soon as you want to do something more than just extruding a curve, Rhino uses more resources to describe the object.

You can start with an extrusion object and when you need to alter it in some way it will automatically convert into a polysurface.

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Hi Nick - see



for more info on Extrusion objects in Rhino.


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Thanks gents

If you’re not interested in Extrusions, as they are lighter in weight but not as easy to edit sometimes,
you could disable them all together and only create polysurfaces.
see this command: