Osprey Raincover

With a 65L Atmos Osprey, the Medium is ample big. Do not buy the large as vendors have Large for 65L. Only reason not 5 stars is no really drenching rain test yet.

Main point here is about the fit. I went all over various sites and while vendors list the Large rain fly for the 65L and larger packs ... you'd make a BIG mistake (er ... pun intended ...) buying a large. The Medium fits very nice.  

See my review of the Crazy Creek Long Back Chair (for end-of-hike luxury and sleeping pad all in one) which the fly fits over together with a backup pair of water shoes tied to bottom of my Atmos 65 (photos included).

I've been in steady rains ... no wind/torrent apocalyptic rains yet -- and it's done perfectly. Easy/quick to put on, tie off, and quick-drying/easy to tuck back into its built-in storage pouch.

Great raincover. If you run into a quick downpour as I did in the Rockies, you can whip this thing out and cover your pack while your hiking or while you've set up camp. If it's raining this thing will clear up room in your vestibule by leaving your pack outside without it being soaked in the morning. Water beads up and is quickly repelled off the fabric, with a few shakes it's dry and good to go.

I had purchased a large for my Aether 85 (around 5000 c.i. if I recall) but a I think a medium would have worked also.

Many feel they would be fine with a garbage bag. True, but if you don't want to look like a hobo and need something a little more durable this does the trick. A good waterproof fabric to have as well in a emergency situation!

I would recommend this item.