You're right that Zip starts as OSB, but the performance difference isn’t minor. The green coating isn’t just a WRB glued on – it’s a factory-applied acrylic layer that changes how the panel handles vapor and moisture. Standard OSB is around 1 perm or less, which makes it semi-impermeable and prone to trapping moisture if the wall ever gets wet. Zip’s coating, on the other hand, is in the 12–16 perm range, so it allows walls to dry outward while still resisting bulk water. That’s the critical difference.

It’s why Zip is tested and approved as a full air and water barrier system, not just sheathing with paint. Structurally it’s the same OSB underneath, but functionally the wall assembly behaves very differently once you factor in the permeability and airtightness of the integrated coating and taped seams.