This sock is seriously thin, almost see through. That said, it is rather warm also. I have injection molded boots, and I can't afford to have a thick sock in them. This sock allows me the best fit possible and also provides plenty of warmth. I've skied brick days in the Kootney's (-20C) and had no issues with foot warmth. The only time my feet were cold was an unreal day in Lake Placid with the wind chill pushing it to -40F, but at that point I was cold all over.
As far as durability, they have lasted me pretty well. My girlfriend robbed 2 of my pairs since she likes to wear them under her fancy leather boots. The pair I have I've skied probably ~40 days in and they are still solid. They do pill a bit but its not performance or comfort impacting. I give them a rinse in the sink with some soap and let them dry over night and I'm ready to ski with them the next day.
Bridgedale Ultra Fit Ski Socks are the thinnest socks I have found. They work great. I prefer a performance fit boot that doesn't allow for thick padded ski socks. These socks fit the bill. I have used many other types of Bridgedale socks and have always been impressed. These are no different.