by Pat Works
A para foil is a nonrigid (textile) airfoil with an aerodynamic cell structure which is inflated by the wind. Ram-air inflation forces the para foil into a classic wing cross-section. Para foils are most commonly constructed out of riposte nylon.
Deployment shock prevented the para foil's immediate acceptance as a parachute. It was not until the addition of a drag canopy on the riser lines (known as a "slider") which slowed their spread that the para foil became a suitable parachute. Compared to a simple round canopy, a para foil parachute has greater steer ability, will glide further and allows greater control of the rate of descent; the parachute format is mechanically a hang glider of the free-flight kite type and such aspects spawned para-glider use.
A slider is a small rectangular piece of fabric with a grommet near each corner used to control the deployment of a "ram-air" parachute. A ram-air parachute has a tendency to open very rapidly. At high velocities, the opening shock from such a rapid deployment can cause damage to the canopy or injury to the jumper. The slider was developed as a way of mitigating this. During deployment, the slider slides down from the canopy to just above the risers. It is slowed by air resistance as it descends and reduces the rate at which the lines can spread and therefore the speed at which the canopy can open and inflate. This invention solved the rapid deployment problem with ram-air designs. Sliders also reduce the chance of the lines twisting to cause a malfunction.