Is it normal for pink insulation to turn black?

That black staining is often caused by air filtration, where the fiberglass acts like a giant furnace filter and traps dust as air moves trough the wall cavity. However, if the wooden studs are stained and the carpet feels damp, you're looking at more than just dirty air. Fiberglass doesn't stop air movement, and when warm, moist interior air hits a cold surface inside that wall, it condenses. That moisture is likely what's discoloring your lumber and soaking into the floor tack strip. If the wood has dark blooming or a fuzzy texture, you're dealing with mold, not just dust. You can test this easily by spraying a small section with a bleach-based cleaner or a dedicated **fungicide**. If the black color foams up or disappears quickly, it's organic growth. If it stays exactly the same, it's just carbon or dirt. But given the dampness you mentioned near the window, I'd bet on a failing window seal or a flashing issue on the exterior.

You relly shouldn't just close this back up. Once moisture gets into those wall cavities, it stays trapped behind the vapor barrier and starts rotting the base plate. Since you alredy have the wall open, pull that insulation out and check the back of the exterior sheathing. Look for water tracks or staining coming from the corners of the window frame. It's much cheaper to fix a flashing leak or replace a few feet of insulation now than it is to replace the structural headers and subfloor once the rot really sets in.

Get yourself a cheap **moisture meter** and poke it into the studs. If the readings are over 15-20%, you've got an active leak that needs to be addressed before you even think about putting new drywall up. If the wood is dry but stained, it might be an old leak that was partially repaired, but that damp carpet suggests the problem is current. Air sealing the gaps with some low-expansion spray foam around the window frame while you have access will also help stop that 'dirt' from coming back.

Listen, if you're seeing staining on the studs and feeling damp carpet, you're way past 'air filtration' territory. Pink Panther R-13 or R-15 is notorious for bypasses, but it doesn't soak a floor. Check your flashing. I’ve seen this a hundred times where the window pan wasn't sloped or they skipped the Zip System tape. If those studs are soft, you're looking at a structural headache. Ditch the fiberglass entirely. Once you find the leak, spray some Concrobium on the lumber and swap in Rockwool Comfortbatt. It’s hydrophobic and won't slump when it gets hit with a little condensation. Don't be the guy who just slaps 6-mil poly over rot.

Are we sure we aren't overthinking the damp carpet? Have you ruled out a simple condensation issue from the window itself dripping down the face of the drywall? I've seen plenty of people tear into thier sheathing looking for a flashing leak when it was relly just a high-humidity room and a single-pane window sweating. Before you go ripping out studs, maybe check if that dampness is just surface-level. If the wood is dark but solid, it might just be old 'ghosting' from when the house was built.

Back in the 70s we called that 'ghosting' when it was just dust, but damp wood is a diffrent animal. If that's a window from the late 90s, I'd bet my last dollar the builder skipped the head flashing and just relied on a bead of caulk that's now dried up and cracked. I’ve seen guys try to 'save' wet fiberglass by letting it air out—don't bother. It loses its loft once it’s been soaked and it’ll never insulate worth a lick again. Pull it all out and look at the sill plate. If you see 'tide lines' on the wood, you’ve got a real leak, not just a sweaty window sweating.

Don't just look at the window. Check if you've got an outlet on that wall too. I've seen 'em act like little chimneys pulling cold air in, and if there's any pipe sweat or a tiny roof leak nearby, it all pools right there on the bottom plate. If that carpet's damp, your tack strip is probly toast. Peel it back and see if the floor's rotted. If it's just the insulation that's nasty, swap it for rockwool. It handles moisture way better than that pink stuff and won't turn into a soggy sponge if things get humid again.