It is possible they are using a more flexible resin or they could have a different fabric inside that has not got the stiffness.  

UD cloth aligned down the fin would make it stiffer not more flexible.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

G'day guys, im needing some help with a project of mine for a friend, he's gotten me to make up a few test sets of free diving flippers, ive pretty much copied a professional set from him, ive gotten the tapper (thin at one end thick at the other) and thickness (1mm to 2mm) correct but I still can't get near the flexability as the professional set, wondering if theres a additive or something i can mix with my infusion resin to make it more flexible as theres seems stupidly flexible, i was also thinking maybe i go away from just using 2x2 twill carbon and maybe add in some unidirectional carbon? Any help will be much appreciated 👍