Hi Len - when you have an open surface instead of a solid, there isn't any automatic way for MoI to know which side is supposed to be the "outside".

It can depend on a numerous factors such as which direction you decided to draw some of the initial curves in (clockwise or counter-clockwise).

The easiest way to get things consistent is to make things into solids before you export them, that gives MoI a way to automatically determine which direction should go to the outside each time.

Otherwise, if you are dealing with non-solids, you'll probably need to flip some things same as what happens in pretty much any modeling system including polygon modeling.

You can either flip things in your polygon modeler, or there is also a Flip command in MoI that you can set up on a keyboard shortcut which you can then trigger to flip which direction is considered the positive normal on an open surface.

- Michael