Tammy writes from Falls Creek, Pennsylvania: "Should fiberglass insulation be replaced after it has gotten wet? There has been a water leak in the attic and the insulation has gotten wet. Will it still insulate well now?"

When fiberglass insulation becomes wet with water, such as most rain and/or supply water, it will temporarily lose a substantial measure of its thermal resistance (R-value). In this case the spaces between the fibers that were previously occupied by air are now occupied by water. Since water is a much better conductor of heat than air, the water presence would cause the insulation to have reduced thermal performance. However, this is only a temporary situation. As soon as the water evaporates and the insulation becomes dry again, it will regain its original performance level.

In addition, since fiberglass insulation does not absorb water, the insulation fibers will not be structurally altered or permanently affected in any other way. The material will essentially be as good as new after it becomes dry, provided it has not lost thickness.

Also, Owens Corning FIBERGLAS Insulation meets ASTM C1338, "Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings."

Now, if the product has been saturated with dirty or contaminated water, Owens Corning recommends that it be replaced. Here is the reasoning: when the water evaporates, deposits of foreign materials that remain may decrease the R-value, and may also give mold and or mildew nourishment and a place to propagate. This growth, and/or odor (Yuck!), may then also be transferred to other building materials.