What Happens to Fiberglass Insulation When It Gets Wet?

Fiberglass insulation works by trapping still air in its fluffy mat. When water fills the spaces between fibers, that air is displaced, and heat moves through much faster. As a result, the insulation's resistance to heat flow, its R-value, falls dramatically, sometimes to near zero while soaked.

The weight of absorbed water also makes the batts or loose-fill settle and compress. Compressed fiberglass has even less trapped air, so it performs worse. Wet insulation can also pull away from the walls or ceiling, leaving gaps that let conditioned air escape and outdoor heat or cold enter.

In some cases, if the water was clean and the insulation dried quickly, it might keep some function. But wet fiberglass often holds moisture in its core, and professional drying equipment may not reach deep enough. The safest route is usually to remove the soaked material.

Removing wet insulation is a messy job. The pros can pull out the affected batts or loose-fill, dispose of them properly, and inspect the surrounding area for moisture damage. They also check the vapor barrier and framing to see if anything else needs attention. If you have insurance, note that policies vary, and your insurer decides what is covered.

If you notice wet insulation after a leak, flood, or overflow, act quickly. The sooner you address it, the less chance of mold and structural damage. You can start by cutting off the water source if it is safe, and removing any soaked items you can handle.

For large areas, hidden moisture, or water that may be contaminated, call local water damage pros. They have the tools to find trapped moisture and dry the space correctly. They can also advise on whether the insulation needs to be replaced, which is often the case.