A design office was assigned to a hearing protector with an adjustable sound level. The noise reduction is hereby realized by small holes (0,1 to 0,8 mm). The big problem was to create a hole of 0,10 mm by injection molding technique. We have engineered a pilot mold based on a No cure No pay agreement. The mold proved to work well. In the meantime, we have shown to produce hearing protector controlled in large numbers.