A steel cord (10) adapted for the reinforcement of rubber products, the steel cord comprises a core (12) and a layer of filaments (14) with round cross-sections twisted around the core (12). The core (12) comprises a flat wire at a waveform, which lies in the plane of the flat wire. The wire is obtainable by first crimping a round wire and thereafter flattening the crimped wire. The filaments of the layer do not substantially contact each other to make spaces between each other to insure adequate rubber penetration into the cords. The steel cord has improvements on elongation at break.