"Andy Asberry" wrote

Jim, you missed a chance to correct a common misconception. Tyvek is
NOT a vapor barrier. It is similar to GoreTex clothing. It allows
vapor to escape while blocking wind and water droplets.

chuckle You are SO right! I was so fixated on the "stiffness factor",
that I didn't even think about the other factor.

A bit more of the history of Tyvec, and the other dozen or so copies, since
it was introduced.

As energy demands drove houses to be tighter, and tighter, some systems like
the synthetic stucco, formed a vapor barrier on the outside of the house.
It was already common practice to put a vapor barrier on the inside of the
walls, either with Kraft faced insulation, or a sheet of plastic. Soon
there were big problems, with walls rotting from the inside out. What vapor
did seep through the walls from the inside, condensed, and could not get
out, because of the barrier on the outside, thus the rot. What was needed
was a product to let the vapor out, without letting the wind blow through,
thus Tyvec was born.
--
Jim in NC