Any bit of plastic wrapper that is wet, such as the plastic wrapper from a bar of soap or a piece of saran wrap that has become wet.
ECTOPLASTIC tends to stick to skin, walls, counters, floors, and anything that isn't a liquid as if it were some sort of spiritual force that is haunting you.
Ida: Ugh, gross!
Doris: What's wrong?
Ida: I've got ECTOPLASTIC stuck to my foot. I shouldn't have unwrapped that soap while I was in the shower.