So you've decided to hit the slopes! If you're a beginner you might be spending a fair amount of time on the ground, so you'll want to make sure you have the perfect pair of pants: not too tight, not too baggy, and definitely waterproof!
Normally winter sports go by a 'three layer' rule of thumb. The first layer pulls moisture away from your skin, the second layer provides insulation to keep you warm and the third layer keeps all the outer cold and moisture out. Snowboarding pants will combine the top two layers, and sometimes even three, into one article of clothing. With outdoor apparel you will get what you pay for, so if you take the more affordable route, pick up some comfy long johns or Under Armour to layer underneath your outer pants.
Snowboard pants are meant to be looser than ski pants. Ski pants will work, but are not designed for the type of riding you will do on a snowboard. With snowboard specific pants you should feel no pinching in the crotch and your knees should have enough room to bend freely and easily. Some riders prefer a pair that will cover the tops of their boots easily, whereas some riders like a skinnier fit at the bottom. If you do decide you like a looser fit towards the bottom, check out Burton Gore-tex Shelter Snowboard Pants--they have a longer outer layer with a tighter fitting second layer so no water will seep in around your boots.
Remember, snowboarding pants are about keeping you dry, not making you look good! Look at the materials and technology in a pair of pants before purchasing.
For beginners or riders who prefer doing a lot of tricks, think about getting some pants with a little padding in the knees and rear areas. This will keep your bruising to a minimum and help you enjoy the day, even when you spend a little time on your bottom. For extra protection check out ButtShield as a layering option.
More important than any other consideration is the waterproofing of the pant. Only consider pants that have sealed seems; otherwise they will just be water resistant, not waterproof, and melting snow will be able to sneak in through the edges. Gore-tex is a breathable, waterproof material manufactured by most larger snowboard apparel brands.
Pockets are cool. No matter what you think about being on the slopes, you will be thankful when you catch an edge and wipe out right where the snow is starting to turn into a lovely medley of water, dirt and slush. Then think about your wallet, your phone and your keys--all safely stowed in a padded, waterproof pocket. House Arcus Snowboard Pants by Grenade have 6 pockets including hand warmer pockets with a key chain.