Testing has shown that fiberglass that has gotten wet recovers its thermal resistance and acoustic properties when it has been allowed to completely dry.
Fiberglass insulation that has gotten wet from rain or snow during installation may recover its full R-value if it is allowed to completely dry out and recover its original thickness. It is, however, very difficult to ascertain whether or not the insulation has dried completely or if it has fully recovered its original thickness if it has gotten wet enough to compact.
It is also important that there are no contaminants in the water that will contribute to mold or mildew growth. If the wet insulation is able to dry completely, if the thickness is able to recover, and it can be ascertained that no contaminants such as mold or mildew have gotten in to the fiberglass, the fiberglass should recover its original R-value and be safe to use.
Fiberglass insulation that has gotten wet from storm waters or flood waters should be removed and replaced. Those sources of water have a high probability of containing contaminants such as mold, mildew, or food sources that might support the growth of mold or mildew. Fiberglass metal building insulation must pass the mold growth test as specified in ASTM C991. Since there is no effective or practical method to determine compliance with that test after insulation has gotten wet from flood or storm water, it is recommended that the insulation be removed and replaced.