I am curious -- having never used a bivy. How would one perform in a snow shelter? Presumably the snow shelter is near the freezing temp, a shelter for 2 or 3 supposedly could be heated with a couple of tea lights. Too warm and then you have water dripping inside the shelter. I'm thinking a bivy is probably waterproof and adds a few degrees of comfort to most sleeping bags. Add a couple of foam pads underneath.
I think you're spot on
The makers of my bivy recommends a candle: The extra heat is mostly welcome, and helps with the condensation problem (you combine extra heat with a little ventilation). I've only briefly tested it, so I won't comment on how well it works.
It depends. If you're laying in it in the middle of snowy field and it's snowing on you? Maybe not so great.
Well, it certainly beats lying in the middle of a snowy field WITHOUT a bivy... Plenty of climbers who has tried something similar when stuck on a naked mountain peak in bad weather and survived because of their bivy.
If you can move just a little bit you can improve the situation a lot by finding somewhere less exposed to the wind. A rock, a trench or just some minor terrain bump makes a huge difference - just make yourself as small as possible behind it.
Or if you were wise enough to build a snow shelter (Igloo style)
Igloos are great, but are not really viable options when you need an emergency shelter because an igloo requires time, labour, thinking and precision. Snow caves are a bit better because they require very little thinking and precision - only time and labour.
My local SAR authorities these days recommends the emergency snow trench, which requires much less time and labour than a regular cave. Find a slope with snow, dig a two foot wide trench, always dig so that you can toss the snow horizontally and downwards OUT OF the trench and down the slope. (The need to move excess snow out of the snow cave is a major part of why digging snow caves are so time consuming - use gravity to your advantage is a HUGE time and energy saver). The trench should be about 3-4 feet high, 2 feet/shoulder width plus a little extra wide and as long as you deem nescessary. When the trench is dug you carve out benches in the side walls. Make a roof by placing skiis, branches or snow shoes on top of the trench and put snow blocks on top of that.
Previous Topic
Index
