Silnylon, a portmanteau of "silicone" and "nylon", is a synthetic fabric used mainly in lightweight outdoor gear.
It is made by impregnating a thin woven nylon fabric with liquid silicone from both sides.
[1] This makes it strong for its weight, as the silicone substantially improves the tear strength.
The variant known as "crisp silnylon" is lighter, but brittle, noisy in movement, and easily torn.
Some versions are made from the stronger nylon 66 and are used for applications like parachutes and hot air balloons.