Hi Myrna, Bob and all, <<have seen a form of Sunbrella which has some sort of vinyl-type finish bonded to inside so it is leakproof. anyone with expeience/knowledge of this or similar fabric>> That is the kind of material we have in our bimini top: vinylized Sunbrella. I forget the trade name, other than Sunbrella something. We really love it. We wanted to put it onto our removable seat covers, too, but were advised against it as it does not breathe and if moisture seeped in through the seams, it could not evaporate and would cause mold to ruin the cushions. These covers are removed when we run the boat from the flybridge, as they cover the seats, seat backs, etc., and are held in place by snaps. So, we used regular Sunbrella on these seat covers. Same exact color, so it all looks identical. We are very happy with them. Wayne M/V Celestial Albin 43 Sundeck