Ski socks are designed to provide three essential needs to your foot: warmth, padding and moisture management. They're usually made from natural fibers such as wool or silk, or a combination of high-tech synthetic fibers, such as acrylic, polyester and lycra.
The fibers commonly used in ski socks are constructed with hollow cores, which provides insulation and holds warmth around your foot. Socks made from cotton or a cotton/polyester blend compress and don't hold hold much warmth next to your skin.
Ski socks also reduce friction and offer protective cushioning where you need it most. They'll often have extra padding on the toe box, heels and on the front of the shin to take up space in the areas where you're most likely to have movement and rubbing inside the boot, which contributes to blisters.
Most importantly, ski socks keep your feet dry by wicking moisture away from your skin. It's this combination of moisture and friction that leads to blisters and general discomfort inside your ski boots.
Buying ski socks
Ski socks are found at most ski shops and specialty outdoor stores. Consider what type of skiing you like to do and make sure you try different brands and fabrics. Try them on with your own boots to make sure that you get the proper fit.