Tyvek is too air permeable for use as a sail. The function of Tyvek is
to allow air to permeate THROUGH the fabric .... and thats why its a
BAD choice for sail material. Its not UV protectect and will oxidize
badly and degrade in the presence of sunlight. Other than when being
applied to the side of a house, when was the first time that you saw
exposed Tyvek on a house .... good reason that you dont as it degrades
quickly when exposed to sunlight (UV).

Go to www.sailrite.com and choose a lightweight & cheap dacron
sailcloth material. BTW.... they also sell sail kits .... already
cut, ****properly broadseamed*** .... just assemble with two sided
sailmakers seam tape, sew together on a homemakers sewing machine and
sail away. Approximately 1/2 or less than a 'store bought' sail (made
by indentured slave-wage workers in the orient). There are a few kit
sail builders on the internet. Why go to all the work of making your
own boat then hoisting poorly cut / inefficient 'crap' to move her?
The sails are just as important as the care that you took when making
the boat.
;-)