By "try to" I meant that you might TRY to sleep in a bivy - but most likely you'll find it difficult to get your golden dose of eight hours of uninterupted sleep and sweet dreams.

Bivys are clammy (vapor barrier) and uninsulated = cold.

When you really, really need them bivy's are worth their weight in gold. By sealing all that vapor inside the bivy you eliminate heat loss from evaporation. Yes, it's clammy, but that's a HUGE heat loss factor that you've eliminated. You also are completely sheltered from wind, rain, sleet and snow. Even though they're uninsulated (= cold) the micro climate inside is MUCH warmer than on the outside. The price you pay is that it's clammy and claustrophobic.

As always, your mileage will vary considerably. Some will sleep through whatever, no matter how clammy. Others have trouble in a regular sleeping bag - not because they're uncomfortable but because it is totally different from their reguar bed.

Face it - if bivy's were comfortable NO ONE would mess around with tents and sleeping bags.