No, not at all. But cotton is a good place to start for if no other reason, it has been tried and accepted by many.
To say it is cheap is an understatement, VERY cheap for the amount you will need.
But also it is a material you are more likely to get a seamstress to make you a set of sails with.
Or, if like Gary, you will do them by hand.
Cotton poplin is that which is light and stretches only in one direction. Gary talks about this in his YouTube instruction video so no point going over it again.
But if you fancy something different you might try rip stop nylon. Rip stop is commonly used for kites and that type is very light compared to other applications. it is also brightly coloured and not at all expensive. It does have to be machine sewn and the same procedure used for cotton works equally well for this.
My sloop Maxine has had a couple of sial sets made from this and it works as well as cotton, . The main difference is, and it may not matter, it doesn’t stretch slightly like cotton poplin.
Another material found on a lot of modern rc kit sailboats is Mylar. This is a plastic sheet used in things like plans etc, but also available in three different thicknesses. it not sewn but stuck together using double-sided filament tape.
This is a whole subject of it’s own and will follow when I get to it.
In the meantime.
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