The difference between round cores and hexa cores is significant. In a guitar string, round cores feel more flexible and have a fatter, more balanced tonal character with longer sustain. Hexa cores are a bit stiffer and are brighter. BlackSmith round core strings are available only for AOT coated acoustic strings at this moment. AOTPRC-1254, AOTPRC-1152 & AOTPRC-1047.