I received 5 yards of the 1/3 oz. polyester fabric from OSK to make a Genki. I found on the straight grain it doesn't stretch it suddenly fails under stress. On the diagonal bias, it stretches significantly IMHO. About the same force applied to both scraps in the picture. Unfortunately I can't compare against Icarex, but this was pretty good effort to break it or stretch it this significantly. But I think this shows pretty well over time it will stretch on the diagonal. For my use it was great, however on a quad line, I think it could stretch.