Which type of fabric is unaffected by moisture and mildew?

Fiberglass is a composite material that is inherently resistant to moisture and mildew. This characteristic makes it an excellent choice for applications such as aircraft coverings and other structures where exposure to environmental elements is a concern. Unlike organic fibers, fiberglass does not absorb water, which means it does not provide an environment for mold or mildew to grow. This resistance contributes to the longevity and durability of components made from fiberglass.

On the other hand, the other fabric options like cotton and linen are natural fibers that can absorb moisture, making them susceptible to mildew and degradation over time when exposed to wet conditions. Polyester, while more resistant to moisture than cotton or linen, is still not completely unaffected by moisture in the way fiberglass is. Therefore, fiberglass stands out as the material least likely to be impacted by moisture and mildew, making it the correct choice for this question.