I bought a used mast that didn't come with a mast bag, anyone made their own? I currently have an old wetsuit sleeve holding them together but want something better. I spotted foil insulation sheets at Bunnings that possibly could be sewn up, but any other ideas out there?
Dunno, if your gunna buy stuff from bunnings, why not just go to one of the windsurf shops and buy a mast bag.
I wouldn't mind betting they're not that expensive 
If you know anyone with a sewing machine it is pretty easy with canvas or dacron and a few strips of the cheapie yoga / camping mats for padding
or hit up the shops, I got a 100 year old NP mast bag from the one piece mast days - it held 4 x 480cm masts (it was LONG!!!) and cut it in half so now it holds 4 new 2-piece masts from 400 - 460
I made mine with old pairs of jeans, just using the legs. A bit of sawing machine, some separation in the middle for the 2 halves, works perfect. Just have to rinse it now and then.
I can't send you a photo now as I am overseas. (Actually working on the Gulf of Mexico and I wish I had my gear right now, 20 knots, not much sea, miles and miles off shore and it's around 32 degC...)
Get some pvc storm water pipe cap the ends and you've got a great mast bag + protector.
Thanks for the feedback guys. I was hoping someone would have said "..go to a plumbers supply as they have cheap rolls of insulation foil tubes"...but that didn't happen....sigh.
However, I do have a domestic sewing machine but it can't handle heavy threads so making anything stronger than a dilly bag is not possible. Mark_australia your idea sounds the most convenient re; old one-piece mast bags cut in half. Pity I chucked my old Gaastra one out years ago, that would have fitted 2 x 2-piece masts. Something will turn up.
New masts usually come with a bag, right? Masts break, but the bags live on. So theoretically there should be almost as many mast bags surviving today as there have ever been masts in all of windsurfing history. 
I have bought all my masts without mast bags, and I have acquired a few, so I am doing my best to prevent a surplus.
Another option is to find a friendly sail-maker that will be able to sew two or three seams straight down the material of your choice, and hopefully for a minimal charge. If its complex I would expect them to say no.
I think I bought my proper mast bag for about $25 from memory, so they a pretty cheap!
