Tow fly (also called fly dust or lint) is an important issue in filter rod production not so much because it's nice to have a clean rod maker but more because it can also affect filter rod quality, for example, when an agglomeration of tow fly soaked with triacetin ends up in a filter rod originating melt holes. This being a very severe defect as it is usually detected and complained by the end consumers. The workplace related issues of this aspect of filter rod manufacturing have been addressed by Stark M., Hengstberger M., Klus H. during the CORESTA Meeting in Vienna in 1995. Usually the consideration of the amount of fly dust is quite subjective. Therefore a method was developed in order to quantify the amount of fly dust which is deposited on the rod maker leading to results in grams per ton of processed filter tow, separating the "dry" zone with short fibers in the blooming unit and the "wet" zone with longer fibers in and after the triacetin booth. A test series was performed which shows that there are highly significant differences in the amount of fly dust depending on differences in the adjustment of the blooming unit, defective parts of the tow treating elements of the machine and the humidity of the air, especially in the jets blowing air on the tow.