Amazingly, a super-thin ultralight sock can be a suitable option even in cold conditions—as long as you've spent big bucks on a nice pair of modern ski boots. Boot liners insulated with products are able to trap hot air against your feet far better than ever before. As long as your liner fits you well and you don’t go out in positively frigid conditions, an ultralight sock is perfectly suitable. The closer, streamlined fit also improves contact with the boots for improved performance.
Regarding durability, ultralight socks fall short of the other options simply by the thickness of their design. We wouldn’t suggest wearing them too much out of the boots. These ultralight options are most popular with those that work hard—hiking or ski touring. Those that require a little extra cushioning or warmth may want to look at the more all-around friendly lightweight category below.
For standard downhill skiers, the lightweight category is a great place to be—with enough cushioning around and under your foot to be comfortable but not so thick and bulky that it feels awkward inside your boot. Those that like to run an ultralight sock for average conditions or for ski touring may want to have a slightly thicker, lightweight option for those chilly days.
Ski socks of old used to fall into this category, but the changes in ski boot technology have made a thicker sock far less important. The benefit of a midweight sock is added cushioning inside a boot, and for those that run cold no matter what, it may be worth having a midweight option. But keep in mind, boot liners are meant to fit snug, so a sock that is too thick can actually restrict blood flow and make your feet even colder. Be sure to dial in your fit just right if you plan to run a thicker, midweight sock. If your boots are too big or you’ve packed out your liners, it could be a viable option.