Poly(ferrocenyldimethylsilane) (PFS) block copolymers form fiberlike micelles by a seeded growth process. This paper describes the effect of adding similar amounts of PFS block copolymers, PFS PDMS and PFS PI, to a common micelle seed. The lengths of the micelles obtained were strongly influenced by the degree of polymerization of the corona-forming blocks. The change in length was due to a change in the number of polymer molecules per unit length of the micelle.