varnished transom to the inflated tubes and dated 1978 it is most likely PVC. I worked for Off Shore Marine in St Thomas in 1980 and they were the dealers for Zodiac in the Caribbean at the time. We repaired quite a few of them after Hugo and I know for a fact that the ones we repaired, mostly from the charter fleets, were PVC. It is possible that your boat was right on the cross over date and that it is Hypalon. It's hard to tell but the PVC boat material doesn't have as deep of a pattern as the Hypalon boats but without them next to each other it would be hard to tell. I can tell you that there were a lot of PVC boats that the transoms fell out of because the black rubber bracket that holds the transom to the tubes kept coming loose needing to be re-glued. If you haven't had any trouble after all these years, it's probably Hypalon.