bought these as an extra precaution when my allegedly waterproof hiking boots did not turn out 100% waterproof.  used these 2 times so far.  once for hiking in rain, once for trail running during a rain.  before i used these, i took another reviewer's advice and put them on, and sat with my feet in a bathtub full of water for 10-15 minutes.  these did not leak.  they did fine on one hike of a couple hours duration during a drizzle rain, and running outdoors for close to an hour, also during drizzle rain - some sections were on a muddy trail, grass, but also pavement.  the outside of the sock definitely does not leak.  they did not give me blisters after a run (i did wear another sock - nylon or polyester - inside them).  however, if your feet are going to sweat, that moisture will not evaporate (or at least not under conditions that i used these).  i did not mind it though.  my feet were warm and not wet from the rain, both times that i used them.  i am women's shoe size 7.5.  i got these a little larger, in case i wanted to wear thicker wool socks inside them.  when washing these - they need to be washed and dried separately (turning them in and out) on the inside, and on the outside, as whatever material they are made of is not permeable.  i'm happy with my purchase and would recommend these, i will be definitely using them again for running in the rain-mud-snowy slush.