Mountain biking clothing should be breathable and wick away the excessive sweat that comes with long, strenuous rides. Since mountain biking is largely a warm-weather sport, the main articles are jerseys and shorts. Jerseys often incorporate fabrics that are lightweight and cool and generally include storage pockets on the back to keep items like energy bars and sunblock easily accessible. Shorts are designed to minimize chafing and wear on the contact points (the inner thighs and backside) of your body.
Colder-weather mountain biking clothing has more insulation and weather protection, but still must be breathable and moisture wicking. Outer shells protect against elements like wind and rain, fleece mid-layers provide warmth and additional insulation, and thin base layers wick moisture and trap body heat.
Early on, mountain biking borrowed styles from road cycling. The sport was very race-driven so the tight Lycra jerseys and shorts from cycling were an easy transition to mountain biking. Lycra clothing was cool, wicked moisture and was aerodynamic and form fitting. While functional, Lycra was never considered stylish.
As different disciplines like freeride began to dominate mountain biking, more relaxed, urban-influenced clothing became popular. Mountain bike clothes that were both stylish and functional hit the market, and items such as baggy shorts, looser jerseys and T-shirts became more the norm. Many times, shorts include a padded insert designed to protect from irritation and injury from extended sitting, and a number of pockets for storage (unlike tight Lycra shorts).
Many major mountain bike manufacturers, including Specialized, Cannondale and Fox, offer clothing lines. Additionally a number of companies specialize in mountain biking clothing, including Pearl Izumi, Zoic and Primal Wear. Clothing lines may include both active performance wear and more casual "after-ride" wear. Most companies offer both a women's and men's line.
A good bike shop will have a selection of jerseys and bike shorts. Mountain biking clothes can also be purchased online either directly from manufacturers or through retailers like REI or Backcountry. Clothing varies in price, but is generally more expensive than generic sportswear, given its specific design.
Comfort is the key for recreational mountain biking. Features within mountain bike clothing are designed to provide maximum comfort and functionality. However, you should always ride in what's comfortable for you. For example, you may find that items like padded inserts are restricting and uncomfortable and might be better off with a regular pair of shorts.