Some Tyvek IS waterproof. Homewrap is not, it breaths. Early in this thread I posted a link to DuPont and it's various versions of Tyvek. The trick with this stuff is finding anything BUT Homewrap out there. The stuff that Priority Mail envelopes are made from is much tougher and water tight, but I've never been able to identify the type of Tyvek they are made from. Tyvek hazmat suits are water tight and puncture resistant. Painter suits breath and are flimsy. Lots of different Tyvek out there.

Silnylon on the other hand is 'spec'd' to be waterproof down to three feet. I read that on the manufacturers literature when I bought a bolt of it a few years ago.
Sometimes 'mist-through' can be confused with condensation building on the inside. I think it's made by more than one mill so who knows what we're getting these days.
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paul, texas KD5IVP