To their defence, I am a very sweaty runner but also I’ve run the same distance with other bras without any chafing.

I also second the person who wrote that the molded cups fit weird and don’t provide separation. I think this is what caused the chafing on my boobs. I have a very average sized chest and bought my regular size but maybe the shape was wrong? The chafe was 2 parallel lines running down my chest between my boobs and curving under them, almost like the letter J. And because I was marathon training, I wasn’t able to take multiple days off to let the cuts heal so they kept getting worse and worse with each run. It is quite the scar.