What is this white powdery substance on our windowsill (pic)?

do you have aluminum windows? This might be oxidizing residue.

No, they are vinyl wrapped wood Anderson windows. Also, there are no boring holes to indicate any insect boring.

Even though there are no visible holes, it does look like insects have been chewing on the vinyl, somewhere, to get to the wood. If you haven't already cleaned this sill, I would collect the residue in a small container and wipe down the sill. If it appears again, you'll be able to see the origin and possibly insects themselves - and don't forget to check above the area and any molding that might be present. At that point, you can decide if you want to call in an exterminator.

It looks like white mold to me. The two primary conditions are warm temperatures and moist, humid air. Dust, laden with dead skin cells and mites, serve as nourishment, while poor air circulation and low light all contribute to mildew’s growth. Preventing mildew from growing in your home requires time and effort to identify probable areas for its occurrence and eliminating the conditions favorable to its growth. Following up with bi-weekly inspections is necessary to identify its presence early and prevent it from thriving.

I agree with Jan Clark. More likely insects eating at the vinyl to get at the wood. Could be termites or carpenter ants. Mold would not be in piles. Oxidation would be a white film on the frames.

Did you figure this out? I have found the same on my vinyl window sill. Vacuumed and wiped it away and no damage to the frame so don’t think bugs are eating the framing. 🤔

I also have this on my window sills in two different rooms. We have bronze colored aluminum windows. Any more thoughts on what this could be?

Insulation? Stuffing from pillows or furniture? I have never seen anything like that. Interested to hear what it is. Is it something to do with the insect laying there? Was he eating something?

Hello, have you figured this out yet? Is it possible the insects got into a sweet treat and were enjoying it on the window sill? Or these are termite sawdust from the vinyl as they are looking to get to the wood

The same exact thing was in my grandmother's apartment. They acted like that they cleaned it when she moved in right and then it came back and I told her not to touch it because I thought that they were doing some kind of like pesticide or something that they should be cleaning it at themselves and I told him to clean it and it came back again and I cleaned it if I would have known better I would have used vinegar my grandmother is in the hospital right now fighting for her life after 3 months and then now on an incubation breathing tube right she was like running circles around me at 81 prior to this place it has definitely definitely not good air circulation definitely moist air conditions like literally they told me just to open up the windows and here it is middle and winter Pennsylvania and it was still up to over a hundred degrees with over a 70° humidity and she said she's never been on oxygen before in her life does anybody know the exact type of that mold because we have been trying to look at what the fungus is that's growing in her lungs and they need to combat it but they can't find the right antibiotic

Not sure, but if you have a School near by, the Science Dept. might be able to help!

Sounds like oxidization of the vinyl.

It looks like some form of mold, you can also see the black specks on the window frame. There must be a source of moisture around there to allow the growth.