You'll need three layers of clothes to stay dry and warm: a base layer to wick away moisture, a mid-layer to keep you warm, and an upper layer to keep the elements out. The base layer should be made of wool or another natural fiber because they're lightweight and breathable. They should also be long-lasting so you don't have to replace them too often. Clothing labels will usually say what material they are made from (such as cotton or polyester). Some people also use synthetic fibers in their base layers because they are more affordable than wool. However, synthetic fibers aren't as durable so you may want to consider replacing them sooner. For warmth, wear layers that contain fibers such as wool, flannel, or acrylic because they are insulating. Avoid wearing thin shirts as an outer layer because they won't protect you from the elements very well and instead risk overheating you. As for protection, choose garments with features such as elbows, knees, and shoulders because these areas are where you might get hit by rocks if you're out on the trail. Make sure any zippers are up and closed because open buttons can cause trapsing insects inside your shirt!