Granite Gear's Cloud Cover Packflys are ultra-lightweight pack covers made from Ripstop Sil-Nylon.
Granite Gear says:
An ultralight pack fly in smaller sizes for ultralight packs and day packs. Made from 30-D Sil Cordura Nylon Ripstop. Designed for packs less than 65 Litres. Check out the Storm Cell if you need a pack fly for a pack above 65 Litres.