The principle of the Ram-Air Multicell Airfoil was conceived in 1963 by Canadian Domina "Dom" C. Jalbert, but serious problems had to be solved before a ram-air canopy could be marketed to the sport parachuting community. Ram-air parafoils are steerable (as are most canopies used for sport parachuting), and have two layers of fabric—top and bottom—connected by airfoil-shaped fabric ribs to form "cells". The cells fill with higher-pressure air from vents that face forward on the leading edge of the airfoil. The fabric is shaped and the parachute lines trimmed under load such that the ballooning fabric inflates into an airfoil shape. This airfoil is sometimes maintained by use of fabric one-way valves called "airlocks". "The first jump of this canopy (a Jalbert Parafoil) was made by International Skydiving Hall of Fame member Paul "Pop" Poppenhager."