I need a new ground sheet as the one I used recently just didn't impress me. This will be double wide (probably) for two under a tarp, though two singles is also an option. I am between Tyvek or Polycryo at the moment but value the input the sheep tampering hordes here can offer ? Thanks Andy
painter's tarp (.05mm) should work better/last longer than the .018 mm window sheathing poly. tyvek is a LOT more durable, but takes up more space in the pack.
I've used a tyvek ground sheet for my tent for a while. Has worked great so far, but like Erik mentioned, it doesn't pack all that well. You can use a dryer without heat and some tennis balls or towels or something to beat the tyvek up. It gets rid of that loud noise it makes when its perfectly flat.
I use tyvek because I use the stuff at work. I use a floor-less tent or a tarp for most of my camping. I used to try and cover the entire floor, but like other folks mentioned it's bulky. So I started cutting it to just fit my bedroll. This is very minor, but I also got tired of the white color. I recently started using an old Australian army tarp. The camo color seems to fit the woods better. And is easier on my eyes. Side note: I was at an esee class a while back, and one of the instructors made a tarp/floor out of tyvek. And he painted the tyvek green with spray paint. It seemed to work pretty well.
While weight might be an issue, I have picked up year old, old model, footprints from REI. Almost five years ago I paid less than $25 for a footprint for an REI Kingdom 6 tent (regular price was over $50). Size is right around 8x10 or maybe closer to 10x10. They are durable because they are designed to go on the ground between the tent and the dirt. Waterproof as well. The time to look is after the first of the year when they come out with their new models and are looking to move last year's inventory. Tyvek is much lighter, though.