Hmm. Interesting.
Seems to me we have 3 options.
1. someone here is telling a fib - highly unlikely as we're all mates with no hidden agendas.
2. bivvi/tent users here don't respire whilst sleeping - highly unlikely. Although they may be Gods of motorcycling, I'm pretty sure they're mortal the rest of the time.
3. there is enough air surrounding the bivvi whilst in the tent to allow it to breath - Most likely. As an experienced tent user I can vouch for plenty of air movement in there.
Interesting when theory meets fact. For my money facts rule and if the theory no longer fits then it needs challenging. After all the World was flat right up to (and slightly beyond) the point some smart ar5e sailed round it!
