Taking on board what Colin has to say, we had a strange reaction between our rear acrylic window and a knitted items while abroad this year.
The white knitted item was resting against the inside of the window for several hours and it has left an area of what looks like white threads on the window although they are not threads but marks.
Months later they are still there. We've tried to remove them but with no effect although we've not got really stuck into cleaning them off yet.
Randa