Hi Psygorn,

re:
> in MOI do we have a command to change normal of the surfaces.

There is a Flip command that can reverse the surface normal direction on an open surface:
https://moi3d.com/4.0/docs/moi_command_reference10.htm#flip

But it won't do anything on a closed solid because solids are automatically oriented with normals pointing outwards from the solid volume.

re:
> although MOI says it is a solid mesh I think it is because of the normal of the faces.)

It's more likely that there's some kind of problem in the trimming boundaries of those faces.

It's hard to know what's going on without being able to test with the actual geometry though, can you please post it or e-mail it to me at moi@moi3d.com?

Thanks, - Michael