An ordinary film, as it seems at first, requires such subtleties in production, because it should have impressive technical characteristics. The film should withstand high voltage to the gap, be completely waterproof and capable of withstanding about one hundred liters of water, per square meter of the area of the canvas. The film should easily withstand blows, easily stretch and then take the previous state. The only, but quite explained drawback — you should not affect the film with sharp objects.