"Silnylon" is a ripstop nylon that's been impregnated with silicon. It's popular for making ultralight backpacking gear and high performance parachutes because it is:
100% waterproof
Impermeable to air flow
Strong & durable
Ultralight & compact
FotoSharp's rain covers are made from silnylon that weighs ~1.3 oz per square yard. White silnylon is semi-transparent (see photos below). This allows you to see the camera's controls when the fabric is held against the camera. You can also shoot a TTL flash thru the cover.
