The helical coiled coil is a well-studied folding motif that can be used for the design of nanometer-sized bioinspired fibrous structures with potential applications as functional materials. A two-component system of coiled coil based model peptides is investigated, which forms, under acidic conditions, uniform, hundreds of nanometers long, and ~2.6 nm thick trimeric alpha-helical fibers. In the absence of the other component and under the same solvent conditions, one model peptide forms beta-sheet-rich amyloid fibrils and the other forms stable trimeric alpha-helical coiled coils, respectively. These observations reveal that the complementary interactions driving helical folding are much stronger here than those promoting the intermolecular beta-sheet formation. The results of this study are important in the context of amyloid inhibition but also open up new avenues for the design of novel fibrous peptidic materials.