The skirt on a River Rover Hovercraft collects air from a special fan and the pressure in that air lifts the hovercraft up. That pressure is actually far less than you might think, less than the difference in air pressure you’d get from taking the lift to the middle floor of the Shard or Empire State Building. In fact the pressure difference from the top to the bottom of a large coffee would be greater!! But that doesn’t mean you can make it out of anything. The skirt material has to be immensely tough to cope with rocks, sticks, sand, mud and ice that it travels over for years at high speed. It has to be able to cope with the strongest tropical sunlight, high temperatures, salt and fresh water, and it has to be able to be repaired even if the craft is in the water. It’s pretty special stuff and it isn’t cheap. But if you were to use the wrong material you might find yourself with a very long walk home!