Thank you for the replies. The 15D/733 is stamped onto a little flap with poppers on the edge of the chute, so obviously it does not refer to the canopy then. It is white nylon (I think) I have not got the room to unfold it to measure the diameter or look for further markings so it is still in a large black sack which it completely fills. If we get a nice day I’ll take it outside and unfold it (but not today rain again!)