I just took a piece of Tyvek Home Wrap (printed right on it, new, wrinkled but not laundered) and ran some water (maybe a pint) into it, and held it up like a bag. The water soaked through and began to drip within a few minutes. This doesn't happen with silnylon unless you apply some pressure. As far as shedding water, Tyvek isn't particularly repellent, that is, water doesn't bead up on it. I'm not sure what accounts for the difference between our experiences...are there different types of Homewrap?