I have had the experience (expense) of various bivis, ex-army,
Kathmandu Trekking, Force 10 and Rab Survival Zone and I can say
without exception the Rab wins hands down.
Initially I thought the material and wieght would give it a very short
life, but without fail it has performed beautifully. Apparently techies
tell me, and I can vouch from experience, gortex isn't a good performer
around the zero mark. I did a Scots May trip with the Rab and although
there was ice and frost on the outside of the bivvi bag, the only damp
areas was around my mouth where the condensation has frozen and then
dripped back on my face ... hmm nice!
The Force Ten, really looks the biz, with a zipped in hood and bug
mesh. But every time I've tried it, too much moisture builds up inside
the bag lining and starts to make my down bag wet. I want to try again
with this one as it is much more heavy duty with a waterproof base and
storage space.
The army one has been great, almost too much space inside, but at times
(gortex I think) a bit too damp in chilly conditions.
The Kathmandu bag, (Milair material) as mentioned in the podcast, is a
tube style affair with an opening at the end, rather than around the
head like the Rab and Army bag. Its a very slim fit and I struggled to
get into a decent sleeping position as the lip kept falling over my
face all the time. It too seemed quite damp halfway through the night.
The Rab is cheap, very light and although a bit on the thin side, has
never let me down. It never leaves my bag, although I want to try the
others once again, I keep coming back to the old favourite.
For those of you suggesting tents, you are missing the point. A
bivvying experience is totally unlike a tent and you need to try it to
understand the pleasures. The air of freedom and views of the ever
changing sky are unique. When weather looks too miserable a small tarp
and a couple of walking poles keeps your head out in the open and you
can have a brew with impunity.
I spoke to Rab last week and the new Survival Zones we have in stock
are grey and they tell me it is even better Pertex than the purple
thing I use. There's only a few of the grey ones around so they tell
me, so if you want one of those, make your mind up soon!
Enjoy!