So I've covered the rucksack and my down insulation, both sleeping bag and insulating jacket. Clearly there was a lot more kit on my back. However, Rondane has made things easy for me. The conditions and the nature of the trip were such that we were either walking in fine weather or sleeping and little else in between. It's not surprising therefore that the overwhelming feeling I had on my return was that rucksack and sleeping system made the biggest difference, shelter and wet weather gear were given so little to do that there's not much to say. Here are the remaining bits of my sleeping system:
TAR Neo Air: The Neo Air has had a mixed press. I can imagine that if, having shelled out the asking price for a Neo Air, you find you've picked up one with a leak you'd feel pretty negative about the product. Especially if you discovered the leak in the field. I have a similar feeling about Alpkit Airic mats. However, I can only call it as I find it. Mine worked perfectly, stayed fully inflated, insulated perfectly well for the conditions and ironed out the stony Rondane surface providing me with superbly comfortable nights sleep. It's got everything you could expect from a mat and provides a solution to the age-old paradox: no longer are optima for pack weight, pack volume and comfort mutually exclusive. It's the ultimate backpackers mat for three of the four seasons. Just how far it could be pushed into the fourth season I have no idea. I havn't used it enough to find its limit. In my humble opinion this mat is worth every penny. TAR should be congratulated for raising the bar. I wonder if their competitors can rise to the challenge? Just one comment about the Neo Air in use: the trick is not to over-inflate it!
MLD eVent Alpine Bivvy: As far as I'm aware, at 360g, the lightest fully weather proof bivvy bag out there. Unfortunately, unless MLD still make them on request, it no longer seems to be available. I'm not sure what Rons reason is for pulling the product but my experience has been largely positive. It's served me well and seen me through several wet (one appallingly wet) night on two extended trips. Nevertheless its a mixed bag (if you'll excuse the pun).
It functions well enough but, after some use I realise I prefer a top opening to a crocodile opening bag. I'm a side sleeper and I find it easier to arrange a breathing hole whilst maximising cover in a top opener. There's also a lot of zip on a crocodile opener and on the MLD the zip isn't covered with a storm flap. Although I've seam sealed everything in sight I wonder if the zip isn't a potential point of water ingress. That's the kind of thought that can keep you awake on a cold, dark, wet night!
The two-layer eVent used by MLD, because the membrane is left exposed, may be less robust than it's three layer cousins. However, a bivvy bag is unlikely to experience the kind of punishment that shell garments do so I don't think this is a big issue. They say eVent is supremely breathable. I don't have any eVent shell garments so can't comment on how it compares to the Goretex fabrics in those clothing applications. Although bivvy bags present the hardest challenge for any breathable fabric (you're in there for hours at a stretch, you may be breathing into the bag and the bags most likely to be fully closed in the conditions least conducive to breathability), eVent seems to do a good job in this application. I've never experienced more than a very light layer of condensation on the top-side of my sleeping bag and only then when I've been forced to close up the bag. When all's said and done though, I would say my Goretex bags perform at least as well. I think eVent is a good choice of fabric for a bivvy but so is Goretex.
I'm less positive about the ground sheet. The Alpine bivvy has a Silnylon base and this, in my experience, is the weakest link as far as moisture ingress is concerned. On a couple of occasions the foot end of my sleeping bag has been damp. I didn't understand this at first but now I'm convinced that the Silnylon has insufficient hydrostatic head to prevent ground water penetration when subject to the pressure of an elbow or knee or suchlike. I go to lengths to keep my sleeping bag away from the ground sheet using knee length mat and rucksack under my legs and feet. If I take care I stay dry. To this end I prefer to place my mat inside the bivvy bag. However, even though I went for the optional extra-wide size, the bag tapers such that thicker mats are a tight squeeze . I just get away with a Neo air short which stops at my knees. A longer air mat would squeeze the loft out of the bottom half of my sleeping bag.
Having spent a lot of time in bivvy bags of one type or another I'm sure they add several degrees to the rating of a sleeping bag. I guess they keep wind at bay and, like a tent, they will trap some dead air around the occupant. It's hard to be sure but my feeling is that this is less true for the MLD bag than for my heavier three layer Goretex bags. I think the fabric is so much lighter and so much more supple that it readily conforms to the contours of a body and so traps less air.
All in all the MLD Alpine Bivvy performs just well enough to keep finding it's way into my pack. If I was anticipating conditions significantly colder, windier, wetter on the ground than those I experienced in Rondane I would be tempted to pack a heavier bag. However, the Alpine Bivvy is just big enough, just weatherproof enough and just warm enough for me. It's just, by the skin of its teeth, good enough for what I do with it. Bivvys are supposed be be "just enough" though aren't they? If lightweight gear is about being just enough to do the job in hand and no more then MLD got have made a very good stab at a lightweight fully weatherproof bivvy bag.