I have purchased a pair of Sums to help with my ultra training. At first I was unsure how they felt as I have got the medium length ones and thought they would be more elasticated, however I can’t complain as they are doing what they say they would and they are still comfy. Around the 15km mark on my runs I feel a slight rub under my left foot but I think if it wasn’t for the Sums I’d probably have a raging blister already. Around the rest of my feet no issues and not sweaty after my runs whatsoever. I will definitely buy a few more pairs throughout the year.