How do you test a bivy bag? Of course, spending one night on a short trip in the mountains!
I was curious and quickly packed the Twillight Bivy by Black Diamond into the backpack and headed for the mountains. Ok, not really mountains, but the Hegau- Volcanoes are around the corner and at least they offer some sporting incentive and another beautiful Micro Adventure.
You can wait a long time for real bad weather, so the test has to take place in rather atypical conditions: pleasantly warm temperatures and drought in March. The setup: the Twillight Bivy, the Exped Downmat sleeping mat and my big Cumulus Teneque down sleeping bag. In addition a Stove for a warm dinner and coffee in the morning. Ready go.
Construction and equipment of the Twillight Bivy
By design, it is a full-fledged 4-season bivy bag for a planned bivouac and activities where a tent would be just too heavy or too much of a good thing. On solo tours and Microadventures anyway, I will take the Twillight Bivy more often in the future because of the low weight.
The very light bivouac sack of approx. 300 grams is made of single-walled NanoShield and promises to be highly water-repellent and breathable. You slip into it from above, there is no side zipper. A mattress fits into it, if it is not too wide, because the bivy bag tapers down in mum form.
The large hood can be completely closed by a mosquito net. I find that a very pleasant possibility, if you do not like snails or spiders at night in the face so much! Or you can close the fabric hood completely and let only a small air hole to breathe, then you should be largely protected from heavy showers.
A nice detail are the two loops, with which you can keep the hood away from the face and fix it with a cord to securing points, branches, etc. When testing the much simpler (and cheaper) Salewa storm , I just noticed the rather unpleasant: lying supine the bivouac sack covers the face, which leads to at least anxiety. This is much better solved in the Black Diamond Twilight. On the one hand, there is the air-permeable mesh at the head end, on the other hand you can get through the guy some "air".
Air permeability an important issue, especially for planned bivouacs. This is not so important in an emergency bivouac, it's all about protection from the weather and not comfort. In simple, non-breathable bivi bags you soon have the problem of condensation. Humans lose at least half a liter of sweat per night. This half liter then collects almost completely in the bivouac sack, which is very unpleasant nights and a pretty wet Sleeping bag in the morning.
For tours with only one night, this is not a major problem, because you can dry the sleeping bag at home. However, this is sometimes not possible with multi-day trips, and the sleeping bag's thermal output is decreasing daily. Therefore, it is important to ventilate and dry the sleeping bag whenever the opportunity presents itself.
During the test sleep at about 5 ° C, although condensed water formed, but in comparison, of course, significantly less than the non-breathable bivouac sack. The ventilation can be easily controlled via the large head opening. If one then still pays to breathe outside and not into the bivouac sack, the condensation formation is limited.
The down sleeping bag was slightly damp in these conditions in the morning and a bit heavier. Down absorbs condensation and does not dry as fast as synthetic fiber sleeping bags. If you want to spend more than one night with the Twilight bivouac sack, you should really rely on synthetic fiber.
For short solo tours and planned bivouacs the bivy bag is well suited and will replace my tent in the future - assuming it will stay halfway dry and I have enough time (and the right weather) to dry the sleeping bag.
In pouring rain, I do not want to have just a bivy bag to protect against the elements, but luckily I have also been spared that.