The basis of dressing for skiing and the majority of outdoor winter sports is dressing in layers. Specifically, you'll need three layers: a base, a mid-layer and an outer layer. Your base layer is responsible for wicking your perspiration away from your body and dispersing it into the air quickly, so that the wetness doesn't sit against your skin. The mid-layer provides most of your warmth. Outerwear serves to keep both water and wind outside while allowing moisture from inside to escape.
The base layer is quite simple. It needs to include tight, thin garments made from materials like merino wool and polyester blends. Base-layer garments include long-sleeved shirts, long johns and underwear. While cotton is a popular material for casual undergarments, it shouldn't be used for skiing. Cotton retains moisture, turning into a cold, wet, heavy mess while you're skiing. Stick with garments designed specifically as skiing/sport base layers. Consider a good pair of warm wool or polyester socks part of your base layer.
The mid-layer is the insulation. This is where you really need to pay attention to how cold the predicted temperatures are for your ski day and how much clothing keeps you comfortable. When in doubt, dress on the warm side and wear multiple heavy garments. You should not try to overheat on the slopes; however, should you get hot, it's much easier to take a shirt off than to try to warm yourself with too little clothing. Mid-layers include garments like pants, sweaters and fleece jackets. Cotton should still be avoided, and materials like fleece and wool will be much more effective. The mid-layer is sometimes included within outerwear in the form of built-in insulation. Different weight materials and varying garments such as jackets, shirts and vests will help to tailor your clothing to the specific conditions of the day.
Outerwear is your ski jacket and ski pants. These need to be waterproof and allow your body to breathe. Waterproof ratings designate a garment's protection factor, and breathability ratings indicate how breathable the garments are. Both indicators range from approximately 5,000 to 30,000; waterproof ratings are provided in millimeters and breathability is provided in grams. The higher the number, the better the rating. Waterproofness relates directly to windproofness, so a high waterproof rating translates to a garment that will knock down wind very effectively. It's not necessary to aim for the highest rating, unless you intend extreme trips, but it's good practice to aim for the mid to upper section of the scale. Consider how wet and heavy the snow is where you ski and how cold and windy it is when choosing outerwear. Built-in venting is an excellent outerwear feature that provides additional cooling and breathability when temperatures rise.
Hats, Gloves and Accessories
No ski ensemble is complete without the right accessories. The parts of your body covered by accessories are the most prone to losing heat and becoming cold and numb. A good pair of skiing gloves should be waterproof and insulated. A removable liner is helpful when it comes to adding or subtracting insulation. A warm winter hat with an extra inner lining around the ears is a second essential accessory of skiing. Many helmets include insulation to both protect your head and keep it warm. Finally, for extremely cold, windy, snowy conditions, cover all parts of your body. Face masks, scarves and neck gaiters will protect the skin that is usually left exposed. Don't forget a good pair of ski goggles or sunglasses to protect your eyes from the sun and wind.