It’s not easy being a weather-resistive barrier (WRB): it has to stop liquid water, be tough and not tear, but also be flexible to wrap around building elements. And it often needs to be vapor-permeable to promote drying.
In the past, manufacturers could cherry-pick the standardized test to use to “qualify.” That’s how we ended up with industry acceptance of perforated and cross-woven housewrap that literally leaks like a sieve.
Now we have a new ASTM “Standard Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers Intended for Mechanical Attachment.” This standard also aligns with the latest version of the ICC-ES Acceptable Criteria (AC) 38–”Acceptance Criteria for Water-Resistive Barriers (PDF).”
BuildingGreen.com’s Peter Yost on the new ASTM E2556 / E2556M – 10: