I used Tyvek for my last LD hike. 2,800 miles on a piece of tyvek i took from a dumpster on a jobsite. The piece is still in good enough shape to be used again. Tyvek is not entirely water proof but it is a good enough vapor barrier to be slept on night after night for 120 nights.
Tyvek has the advantage of being able to be written on with a felt pen. While I used it to make a sign to aid my resupplies other hikers drew big colored dots on theirs so they could play trail "twister".
Tyvek will also deflect a lot of the sun's heat, provide shade, and is relatively rain resistant even after it's beat to hell.
My favorite trick was to wrap my legs in my tyvek ground sheet during breaks in windy cold weather. It actually saved me from needing to carry pants on the hike. Since I was always in my sleeping bag when not hiking and hiking 14 hours a day the Tyvek filled the need for leg comfort in between times.
A Poly Cro ground sheet is 1.5 ounces and cost money.
My Tyvek Ground sheet was 5 ounces.. and free from the trash.
As a new construction plumber I have met a lot of carpenters. Despite their appearance and demeanor they are, for the most part, a friendly bunch. Many of them are outdoors types themselves.. fishermen, hunters, etc. If you ask nicely they will no doubt let you have Tyvek Scraps or even cut you a piece off the roll. So don't be afraid to approach them on a jobsite where you see the white tyvek home wrap going on.
