Board Thread:Game Discussion/@comment-130.14.254.26-20130708130531/@comment-4199297-20130709160446

If your fusion result is a craftable armor, leveling it up does unlock +. (so you could for ex. get a headstart on the big four by fusing armors into the big four's non-plus version before you have the materials to craft them.)

Non-craftable armor: even if it did unlock +, what would be the use if you can't craft it?.. ;-P   AFAIK non-craftable "plus" armor can only be gotten from the chests. (or special events I guess, such as getting Black Kaleidoscopic+ if you craft the 4 epic dragon boss armors+ ...)