The duct tape is necessary to make flaps or other perturbating elements on boomerangs blades. This kind of tape is the only one robust enough to be durable on boomerangs, despite rain and sun.
It will allow testing many tunes of leading or trailing edges, to adapt the boomerang on the field, to the weather conditions. It is very easy to cut by hand, which allows last-minute tuning during competitions !
We selected the best, a Tesa tape, 19mm wide, 0.26mm thick. It is sold in a 50m roll. Colour depending on stock.