When you are fusing glass you have to know the COE....coefficiency of expansion. The rate at which the glass melts and cools. In fusing, we work with either 90COE or 96 COE. If making lampworked beads, we work in 90COE or 104COE. They must be the same or will crack when heating up or cooling down. In stained glass it does not matter since heat is not involved. This is why fusible glass costs more, because it has been tested and rated to assure the consumer it is compatible with the glass the fuser may put it with.