Getting nice squares with subsurf turned on

I’m modeling a car right now using the subsurf modifier. Having no problems with anything except for the windows. They should have hard edges. When I use a different materials for the windows I end up with this(see pics). Whats the secret to applying a subsurf but not having it affect certain areas of the mesh? I thought that the side windows turned out decent, they should still be more square I fixed them by extruding the edges out alittle, but the back windows look horrible I can’t figure out how to fix them.



Head over to this URL and have a good read:

It is written for Lightwave but is equally relevant to Blender.

Hope this helps?

Kindest Regards,