If you mean not to put any fabric around the rigid fiberglass, then yes, it will get itchy as hell. However, it will also stay very fragile and probably become ruined after a couple of sessions. However, if you make a decent (wooden for example) frame, and cover the fiberglass with fabric, the itchyness won't be an issue as the actual fibers won't come through the fabric.
I myself have used rockwool instead, because the rockwool panels were a little more rigid than the fiberglass panels I could get. However, I still have to wrap them in fabric to get rid of the itchyness (plus it looks a lot better) and the frame is to support it, because in this case riggid isn't really that riggid at all. It's riggid enough stand again't a wall without collapsing, but it's not riggid enough to not break when pushing my hand on it.
I suggest either getting the most riggid stuff you can find, and then treat it with fabric and a decent frame at the very least. Your only other option (that I can think of) is getting actual acoustic panels.
