Choosing the best house wrap is a short-term decision that can have significant long-term effects. Effective air and water holdout can contribute to both structural durability and energy efficiency, while the optimal level of vapor permeability can allow walls to dry more quickly if water does get in, to help prevent mold and rot.
Based on cost alone, a perforated wrap can look like a bargain versus DuPont™ Tyvek® weather barrier. But a closer look at the material science inside each product, and the resulting performance comparison tells a different story.
For long-term value, Tyvek® weather barriers provide protection without the trade-off between water resistance and vapor permeability, unlike perforated wraps
The leading perforated wraps on the market today are made of a coarse, woven polypropylene slit film. This weave structure is inherently poor for resisting air and water infiltration. To address this weakness, a thin polypropylene film coating is added to seal the breaches and lock the weave in place.
But solving one problem only creates another. The result is essentially a non-breathable vapor barrier, which is not desirable for a house wrap. To address this, thousands of tiny holes or “micro-perforations” are then poked through the film.
These holes do allow a certain amount of moisture vapor to pass through. But the tradeoff is that they also compromise the wrap’s ability to resist air and water penetration. This is the perennial dilemma of perforated house wraps: there is always a trade-off between air resistance and water resistance on one hand, and moisture vapor permeability on the other.
Unlike perforated wraps, DuPont™ Tyvek® weather barriers are made of a continuous, nonwoven, non-perforated sheet. The sheet is created by spinning extremely fine, continuous, high-density polyethylene (HDPE) fibers that are not fused together, to form a strong, uniform web. So instead of holes, it creates a fibrous structure with millions of tiny pores that are extremely effective at holding out bulk water and air penetration, while allowing moisture vapor to pass through.
Material science is persuasive in choosing the best house wrap, but nothing is more important than performance. Compared to perforated wraps, there are no performance tradeoffs with DuPont™ Tyvek®HomeWrap®.
In independent testing conducted in accordance with the Hydrostatic Head Test (AATCC-127), DuPont™ Tyvek®HomeWrap® demonstrated 17 times the water holdout capability of a leading perforated wrap. This measure is a significant indicator of building envelope effectiveness.
The same testing also revealed a considerable difference in comparative moisture vapor transmission. Tyvek®HomeWrap® exhibited nearly four times the vapor permeability of perforated house wrap, which can only allow vapor to pass through punched holes. The superior vapor permeability of Tyvek® HomeWrap® correlates to decreased wall cavity drying times, and a reduced potential for mold and wood damage.
In separate ASTM E-283 testing (at 75PA or 1.57 PSF), Tyvek® HomeWrap® also showed superior performance in the area of air resistance. This is significant because preventing air infiltration in the wall cavity is a key factor in allowing insulation to perform to its installed R-value. And insulation that performs effectively can reduce the long-term energy costs of heating and cooling the home.
View a full DuPont Building Science Bulleting article for more information.