For a ground cloth, I'm wondering if anyone has tried both of these products?

Which do you think works best & why?

It looks like the Polycryo might be lighter. I could be wrong. My math is major fuzzy.

Here's a link to the Polycryo: http://gossamergear.com/shelters/she...th-large.html#

Link to Tyvek: http://questoutfitters.com/uncoated_fabrics.htm#TYVEK

Or maybe something new I've not heard about yet..