@musashidan Those red UV islands don't need to be flipped? Every time I have UV islands like that, the faces end up flipped for Substance Painter, and Painter's back face culling makes it so these faces don't show up unless you're looking at them from the wrong side of the face.
you probably have that idea because you are doing environment art, using tileable materials. For non-tileable materials flipped faces don't make a difference. I regularly flip shells if its gonna make them fit neater and I know they aren't gonna need any tileable texture or pattern applied to them. also a meshes face's…