Osprey Ultralight Raincover

Durable water repellant can get you pretty far, but for downpours and wetter conditions, this ultralight raincover will keep you backpacking, trekking or hiking pack protected and dry. Comes in three sizes to fit most outdoor packs. 
Ultralight Raincover Extra Large – Fits 75-110 liter packs
Ultralight Raincover Large – Fits 50-75 liter packs
Ultralight Raincover Medium – Fits 30-50 liter packs