Bicycle shorts must serve a very important function. Otherwise, why would anybody wear such a skintight atrocity in public?
It turns out that "skintight" is the key word. Bicycle shorts actually are designed to act as a second skin. They are made of synthetic polyester materials called "wicking" fabrics that draw moisture away from the skin. Wicking fabrics helps keep your body cool during long, hot rides. And in cold weather, moisture trapped on your skin can actually lead to hypothermia [source: REI].
Bicycle shorts play another important role: protecting your privates. During long rides, some very sensitive body parts rub against the seat of the bike. Bike shorts have a special panel called the chamois that's designed to reduce friction and wick moisture away from these areas.
While we're on the topic, bicycle shorts aren't meant to be worn with underwear, particularly cotton underwear, which traps moisture [source: Schloss].
Mountain bikers often opt for baggier bike shorts instead of the skin-tight versions. Road racers like the super tight shorts because they cut down on wind resistance. That's not as much of a concern for mountain bikers [source: Schloss]. These baggy shorts still have an inner layer that holds tightly to the skin to reduce friction and control moisture. But baggy shorts offer better protection during a fall and are more durable.
Mountain biking jerseys are mostly about temperature control. For warm-weather rides, look for a lightweight polyester material that wicks away moisture and has zippers in the front for when things get really sweaty. For winter riding, think layers, layers, layers. You want a wicking layer close to the skin, then an insulating layer like a fleece, and then a waterproof shell [source: REI].
If you're going to try downhill racing or freeriding, you'll need more than a thin layer of polyester to protect you. In the next section, we talk about mountain biking armor.