Originally Posted by
Norway
Are you referring to the Rab 2 person shelters? I don't like them because they are configured for sitting, you cannot lie down in them if you have an extended stay. I am looking at Ortovox bivy Pro myself as I would like to replace my current Jerven Original with something visible.
When I look at dimensions for myself, I want 120-140 cm width (so you can use a flask or heater inside) and length minimum 140cm and preferably 220cm. Strenght and weight is usually connected, strong multiuse ones weighs upwards to 1 kg, lighter use ones about 500 grams and single use shelters such as a plastic bin bag can be well under 0,1. On simple trips where it is just a matter of dodging a little weather or keeping a bit more heat whilst waiting for light, I am perfectly happy to use a plastic bag. Just poke a vent right in front of your face when you sit into it and don't go in/out more than you need to as they can collapse/rip.
The heavy expedition styles have more control over ventilation, but all of them will have condensation. That is the price you pay for arresting an air bubble around you, the payoff is that you spend less energy heating that air and the weather cannot get to you directly.
If you want to sleep in a bivvy bag, place your head towards shelter like a rock or a tree with feet pointing into the wind. (Not always possible). Put your sleeping pad, grass, whatever gets you off the ground INSIDE the bag. Tie the head end of the triangle you create as high as you can, stretch out the foot end and stake if able. Zip up to height of boots/above your head.
This really helps get rid of condensation and keeps you warm enough to avoid injury. Cross your legs to lock thighs, put hands into groin or armpits and doze. Wiggle/rock body when cold bites you, but do not "open" your position. I've spent night like that in New Zealand (shelter, wool shirt, no sleeping bag), benefit is that you can go very light drawback is significant sleep deprivation.
Together with a foam pad, this or a poncho can greatly increase your glassing comfort. If we look at weight-vs-comfort-offered, it is very difficult to beat. It certainly outperforms 0,5 kg insulation jacket for glassing...
It's actually THE very same bag I carried back then so they last a long time. Together with some nylon thread and elastic bungee it can be quite useful.