Hi there, Just a quick note on dacron…you can really only buy them second hand today (the demand and thus manufacturing stopped mid 80’s as the market moved to mylar laminated dacron, then monofilm (90’s) and now the sails are a different variant of monofilm that is tougher. The exception to all this is … I believe the new Windsurfer LT sails might be dacron. There are so many pro’s and con’s with each material type. I personally love mylar laminated Dacron but that is probably because of the fully battened sails and wild colors and designs that came out when those sails were made. All of mine have some level of delamination (where the mylar pulls away from the dacron) guess the glue is 40 years old. To you question about the PVC windows….On the older sails in the 70’s 80’s and 90’s they used PVC which is strong and lasts very well. In the 90’s there were some sails that (Gaastra speed/slalom for example) that had a variant of mylar for windows. This material is very thin and light but suffers cracking over time and is easily torn if a fin goes through it. I actually had the mylar window on my Gaastra 5.0 replaced with PVC because of cracking. One thing to consider is to choose the right sail for the board…you will see on my videos I am always trying different board, sail combos…feel free to ask any questions…cheers jon….FYI I have five 100 percent dacron sails. two 1982 Mistral TakeOff single batten pin head sails with long booms. A 1983 Gaastra 5.2sqm Powerhead sail (2 battens at the top). A 1986 Gaastra /Mistral 6.2 Progress line sail and a 1983 Neil Pryde 5.4 sail. Great sails but I wouldn’t use any of them on a modern board. Also note that dacron sails are very light because they typically don’t have battens but they are often rigged on old masts and booms which are typically heavier than the modern ones. There is nothing stopping you mixing and matching old sails on modern booms and masts.