Within the "HaLo-Filter" project (High-absorption Low-pressure-loss Filter) a new manufacturing processes for the production of energy-efficient fine dust air filter media with high dust storage capacity is developed. The basis is a multifilament yarn with individual fibre diameters down to 800 nm that is manufactured using the Island-in-the-Sea melt spinning process. This yarn is crimpable and due to a water-soluble Sea-component an endless crimped micro/nano fibre yarn can be gained for production of a highly porous filter medium. Here, due to the difference in overall Islands-in-the-Sea fibre diameter compared to single Island fibre diameter the crimping takes part under different conditions and leads to different crimping quality. Especially the influence of the needed bending radius has to be taken into account. In addition, the position of the Island fibres within one filament leads to different bending radii. These influences will be discussed theoretically and proven with optical methods.