I have 2 bivys-One is a North Face Ultra light climbing goretex bivisac which is excellent and a green British Army Bivisac which if you read the stamped label on the inside says.............'The North Face'! The Army one is harder wearing and a simpler design ie no vents, zips, flaps etc and both are equally well made and work for me. The British army one is not as close fitting but is a simple big bag with a toggle closing allowing kit to come in with you. Also I find I roll around inside the army bag but in the Civi version it rolls with you. I got mine from Strikeforce supplies for £40ish.
