Great Emergency Bivy - Never to be repacked to its original size
This is a great emergency bivy for the bottom of your pack or day pack. So small you may forget you have it. It is much more durable than the foil space blankets most folks keep for such contingencies. Further, it is superb lightweight bivy for daily use to keep your 900 fill down bag perfectly dry inside a tent with condensation and or leaks. But forewarned - once you open it for the first time from its "factory compressed" state - stand back. It is liken to opening a can of Pillsbury biscuits at altitude - almost explodes from stuff sack - never to be repacked again its original mico-small bag. Once you are over that - get a larger stuff sack and it compresses down to a pretty small size. JC

Spectacular Ultralight Backpacking Option
I just did a 2 day backpack with the MSR E-Bivy. I'm really jazzed about it. I recommend it for ultralight backpacking. My pack was so light after replacing my tent with this. It adds some warmth - I was a little warm in my 40 degree sleeping bag on a 35 degree night. The weather threatened for rain so I kept the head flap over my face all night. I was able to breathe fine . So I intend to use this on all my backpacking trips.