You could still leave your bags unzipped in the bivy until one of you got colder. that person could then zip up their bag while the other stayed 'comfortable' <img src="/forums/images/graemlins/smirk.gif" alt="" /> I'm thinking you know how 2 people in the same bed sleep cold and hot. This would give you both good convection protection with lighter bags; and with a zipper on both sides you could answer Nature's call without awakening the other person <img src="/forums/images/graemlins/smirk.gif" alt="" />
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PEPPER SPRAY AIN'T BRAINS IN A CAN!