The high relative humidity and warm temperatures in the crawl space allow for microbial growth to occur. Mold loves the paper backing of fiberglass insulation it's referred to as mold candy. The mildewed insulation is sitting right against the floor of your home and impacting the indoor air quality of your home. As air Is pulled up into your home through the stack effect, 50% of the air in your home comes from the crawl space, and its bringing pollutants and allergens with it impacting the air quality of your home.