Scroll down the Kickstarter page for a very readable explanation: "The secret behind the Windcatcher's amazing speed of inflation is its ability to leverage th

Scroll down the Kickstarter page for a very readable explanation: "The secret behind the Windcatcher's amazing speed of inflation is its ability to leverage the awesome properties of air. Simply put, the two most important properties are: - Fast moving air has lower air pressure than slow moving air - Air with higher pressure will be drawn to areas of lower pressure When you blow into the Windcatcher you create a stream of fast moving, low pressure air. Because it has a higher air pressure, the surrounding air is sucked into the low pressure air stream. As a result, the air entering the Windcatcher is at least 10 to 15 times greater than the air you expelled from your lungs."