Tyvek is a moisture-barrier housewrap made of High Density Polyethylene (HDPE) that allows ?breathing? but not moisture penetration. It is installed on the exterior of a building just under the siding to keep moisture from entering into the wall system, where it can form mold. Tyvek and other polyethylene housewraps are green materials in the sense that they are very effective at protecting indoor air from mold contamination. They also improve a home?s energy efficiency by preventing air leaks.
I am not aware of a green replacement for moisture-barrier housewrap that has the same performance as polyethylene-based products. One alternative would be a 15-lb. asphalt felt similar to what is used on roofing. The woven materials are typically organic, but they are impregnated with asphalt, a petroleum product. Also, you run a higher risk of mold formation when you incorporate organics into a sealed wall system. So you have a trade-off: Do you use Tyvek, a petroleum-based product that could emit small amounts of vapors and that may have a large manufacturing impact on the environment? Or do you use an alternative system that may not be proven and that has other risks, like an increased probability of harboring mold?
If you were beginning new construction, another alternative would be to build with Insulating Concrete Forms (ICFs) or Structural Insulated Panels (SIPs). I?m a fan of ICFs?a concrete wall is great at slowing moisture ingress. The energy efficiency of these systems makes them my first choice, but it sounds like this is a remodeling project, so ICFs and SIPs are probably not an option. Also, because some of these products gain their moisture resistance by using closed-cell polystyrene foam, you are left trying to determine if polystyrene is better than polyethylene.
In the end, I think the benefits of Tyvek outweigh the other concerns. The material is on the exterior and there is relatively little risk of offgassing. Polyethylene plastics are widely recyclable. Additionally, DuPont has put great effort into insuring that its manufacturing process for Tyvek has a small environmental footprint.