lightest tarp possible

5x7, 8x8...55 gallon trash bag, Tyvek, 6 mil plastic....
what is the lightest weight possible?
poncho? like frog togs? what's best?
I like Tyvek, but I need subdued color. $ is also an issue.

Take a look at the "Parcho" from Quest Outfitters as a possibility. It comes as a kit with all materials and pattern and needs to be sewn. But, the sewing is not difficult and the Parcho works better for me than any previous piece of rainwear that I've had. It combines the features of a poncho, a rain jacket and a pack cover. The Parcho keeps you and your pack dry and is not terribly prone to internal condensation. I also use it as a ground cloth with my Zpacks Solo with a mesh floor. My Parcho, cut for a lightweight pack, weighs 7 oz. The cost of a complete kit is $50.

Absolutely the lightest would be cuben fiber (see ZPacks), but it's definitely not for those of us of modest means! I'd suggest sewing your own out of a high quality silnylon--It will hold up well for years (unlike plastic or other el cheapo substitutes) for years, but won't break the bank.

Size: The problem with a smaller size tarp is rain blowing in under it, requiring a bivy to protect your sleeping bag, which adds to to both price and weight. In other words, you might as well start with a tarp that's large enough that you can lower the sides-to the ground if necessary-in really nasty weather and don't need a bivy.

Zpacks pocket tarp. 4oz. 200 bucks

Heard over about the Parcho before, good to hear it is a good one against internal condensation.