Tyvek

Fernando (standing) and Carlos (ladder) finish applying the house's windbreaker. Using a wrap like Tyvek or felt prevents airflow in the places you can't control it. The idea is to totally own the airflow through your house using windows, doors, HVAC and exhaust fans.

Tyvek is essentially plastic, so it's not a very green product from a petroleum-use point of view, but the added energy efficiency for the life of the home is well worth it. If you've ever seen this stuff close-up you've probably noticed that it's a mesh, not an impermeable plastic membrane. That's important because we don't want to trap moisture against the wood of the house, which would cause accelerated wet rot and eventual building collapse. This has been a big problem with homes wrapped in EIFS and several other hardboard and composite sidings. In Portland alone, there are quite a few class action lawsuits open against manufacturers of house weather barrier materials that have kept the cold out, but the water in.