Ghasts are by nature invisible, and their appearance is unanimously accompanied by clothing of some sort. To become tangible, a ghost must first resonate with a physical object which it becomes bonded to; in the case of a ghast, this object is clothing. From then on, even its invisible body is physical.
Ghasts can be wounded, but do not bleed. Weapons become "embedded" in their invisible flesh and deal a sort of converted spiritual damage to their souls. These wounds can be healed, but given a wound that would be fatal to any human, the ghast dies. Upon this second death, the ghast becomes separated from its bound clothing and returns to being a ghost.