This comes courtesy Sam G.:
Wing suit diving encompasses the mechanical idea that, by increasing the body's surface area, you can slow down your rate of descent and increase your horizontal velocity. These suits consists of three "webs": two covering the area between the right and left arms and the thigh and the third between the jumper's two legs. Once the suits are fully opened, experienced wing suit divers can reach a glide ratio of almost 3 meters (meaning that for every meter fallen, three meters are traveled horizontally). A typical skydiver's vertical terminal velocity is usually between 110-140 mph however experienced wing suit jumpers can bring their vertical velocity to less than 25 mph and their horizontal velocities above 150 mph. In this video Jeb Corliss pilots his body in such a way that he is able to come down very close to a grassy field before flying into a large canyon. Diver's can control their ratio of forward velocity to vertical velocity by changing the shape of their body at the torso, shoulders, and knees. These different movements control the tension that is put on the suit from air friction and help to control the descent.