Barks wrote:As mentioned above, goretex type bivvy bags are only ‘breathable’ when they are dry, once rain or heavy dew is on them condensation will quickly build up inside and you will get very clammy and cold - Goretex type material is not the wonder material that many people think it is. The army system uses a shelter sheet to keep the worst of the moisture off and the bag itself keeps the wind off and warmth in. As for the mat, if you have a Thermarest neoair inflatable type then keep it inside the bag (it is more expensive than the bivvy bag in any case and can easily puncture) and use a ground sheet (a piece of builders Tyvek works very well) to minimise risk of sharp stones, briars or thorns damaging the bag itself. If you use a closed cell foam mat then that can work well underneath but there still remains a tendency to roll off it. Army bivvy bag plus shelter sheet plus tyvek groundsheet still come in at around nearly 1kg and will cost under £100 if you shop around. Ultra lightweight tents can come in at around 1.2kg with poke system and will cost at least over double that but you do get an encllosed space away from bugs and better protection in very bad weather. You can also get very lightweight mesh inner tents that will go under a shelter sheet that are much more comfortable than bivvy bags and more versatile. DD Hammocks are a good site to look at to get the idea with lots of informative instructional video clips of the different options.
Yes a lot of truth I think in your comments about condensation. I slept in my army bivi in a wood once, September or October. No rain that I was aware of. But the next morning my sleeping bag was rather seriously wet/damp on the outside. Luckily I had stopped just short of my intended campsite, so I just laid the bag over the farm gate to dry in the sun. I do have a tarp/shelter but need to work on the set-up. Your post gave me the kick I need. Thanks.