There's not a top to them, but I have these (S5's) and like them, work well as a vocal booth made from gobos. May not work with tall singers unless you rig something up. Very portable and can be used as a makeshift bass trap (tho not as good as RealTraps) if you set up in a corner...
They're fiberglass within cloth covering.
http://www.clearsonic.com/sorber.htm