Do foam core wings build heavier or lighter than built up wings?

I'm contemplating building Miss Norway to learn a new construction technique, and use for sportsman pattern along with my or instead of my Ultra Sport. It is supposed to handle crosswinds exeptionally well (according to RC Modeler Magazine's "Flight Training Course" for pattern{Antiquated now, but still usefull.}).

If I can learn how to cut foam cores well, maybe it might be worth my while to cut foam cores for the Ultra Sport as well.

Upon browsing the archives on this subject, there really wasn't much that jumped out at me as to this particular question.