I've been finding this material all around my house for the last six months. To give you some perspective, the sample below is about 2 inches by 1 inch. The sizes of the pieces I find vary considerably in size from less than 1 inch to almost a square foot. The larger pieces tend to be flat like a layer. Other houses in the neighborhood don't seem to have this so it seems to come from our house.
I live in a house that has been converted into two condos and the other unit had construction done last year. Most was internal, but they did have a sky light put in. I wonder if the construction left a hole somewhere that allows an animal to get in a retrieve this material.
Any idea what it is? It feels synthetic. Figuring out what it is should hopefully help us find the problem and fix it!