Jay J attributes a bit more to Tyvek than it can actually do, The material is water resistant, but it allows gases, such as air to pass through along with dust as small as 2 microns in size - both ways. It will not keep water vapor inside or outside. Hoswever if allowed to be below the dewpoint, it will collect moisture on the surface. This would be the source for growth; but that is the problem with all materials.
Tyvek's ability to pass moisture while providing water protection is one of its greatest assets. It breathes in both directions, but usually, during the winter more moisture in the form of relative humidity is produced inside than out, so Tyvek allows moisture to pass to the outside while it resists some of the wind force that would allow cold air to pass inside.
Abrasion Resistant--DuPont TyvekŪ protects critical surfaces from scratches and nicks during shipping and storage. With the ability to filter out 98% of dust particles as small as two microns, covers made of DuPont TyvekŪ also shield from scratches and stains due to dirt, dust, and bird droppings.
Breathable--DuPont TyvekŪ is naturally breathable, so paint vapors can continue to offgas through the material's microscopic pores. This means that covers can be put on after painting--without the risk of ghosting.
Water & Chemical Resistant--Microscopic openings are small enough to resist water and chemical penetration. Wet or dry, DuPont TyvekŪ retains its properties and remains inert to most chemicals, including acids, bases, and salts.