If I want to provide 5 Velux windows with new Seals, I would actually like in advance the amount of material can estimate that I need. Unfortunately, there is the statement '1-3 Window "insufficient. Then a foam filter is supplied, for my windows have no use. I could not find foam filter despite accurate Search- at least when screwed Velux Rollos-. As the instructions only consists of pictograms, must be thought of statements in this regard ...