Ill have to look into that. Mine I got from a running mag 4 or 5 years ago. I read some of the posts on the barefoot. Ill add my 2 pennies that it flat out works. I don't do barefoot 100% of the time but did go to minimalist shoes and adjusted my stride from a heal to toe to short stride ball to toe and the lower back and knee pain i used to get from running on anything other than grass disappeared within a couple weeks. Also for guys starting don't jump into it too quick. Most of the research I did recommend easing into it to develop callouses and to build the ligaments in the foot up as they most likely weren't up to par for the change from heavily cupped heal supports in most running shoes to no support.