http://leacree.com/home/products/index/class/2.html
LEACREE Air Suspension Springs are composed of a highly durable rubber and plastic bag. The bags are inflated to precise pressures to mimic the compression ratio of traditional coil springs. Air suspension Products restore ride height, stability, and control just like LEACREE’s conventional coil spring based products but with the added benefits of near-infinite adjust ability and load leveling capabilities.