I Need Help With a Bivy Issue

[Monte Masterson]

John, in temps above freezing and with a 30 degree or warmer bag I place a torso length NeoAir X-Lite inside of the bivy. But in colder temps with a full length NeoAir X-Therm and lower rated bag I place the pad underneath and outside of the bivy.

To get the bivy over the bag I get inside of the bag first and simply pull the bivy over. Just roll the bivy up beforehand. Some prefer a zippered bivy for easier entry and exit such as an MLD FKT, but the MB Dry Tec is fine with me. I like simplicity.

[J-L]

Thanks, Monte. Very helpful. I might have to give it a try this winter. Seems perfect for most Arizona winter nights.

[Monte Masterson]

I of course place polycro underneath when I shimmy into the bivy while in my bag to protect the bag from dirt of snags. And I leave the polycro underneath unless it rains. If it starts raining I pull the polycro away in order to keep water from pooling up. Better to let the rain permeate into the ground.

I also pair the MB Dry-Tec WPB bivy up with a 7 oz silk bag liner as part of an XUL warm weather kit. The silk is a little heavier grade than most and I find it provides more warmth than fleece, cotton or even the 8.7 oz S2S Reactor bag liner (way overrated). I’m going to post a thread on the XUL kit soon and I’ll provide pics. It’s more for fastpacking/FKT or just in case day hikes.

[John S.]

Monte, I can’t wait to know what brand/model the 7 oz. silk bag is…can we know now?..lol

[Monte Masterson]

It’s a Terramar Thermasilk, but unfortunately I can’t find any on the internet nowadays. I bought mine off Gearswap from Bill in Roswell last year. When I got it the liner weighed about 8.5 oz with a pillow holder extension, however I removed the extension and modified it with a draw string closure.

There are some silk liners out there that are VERY light and some others that are mid weight. REI has a Cocoon silk liner marked way down right now and it weighs 4.8 oz. https://www.rei.com/product/850427/cocoon-silk-mummy-liner

Montbell Euro has a beautiful silk liner that weighs about 6.3 oz and that is probably the best choice, but Montbell US doesn’t have them. https://euro.montbell.com/products/disp.php?cat_id=14007&p_id=1121582

[J-L]

Another possible option could be an Alpha Direct liner bag. It would probably be a lot warmer than silk. Timmermade has an overbag that weighs 9 oz. Some custom dimensions (for use as a liner in a bivy) could bring that weight down further:

https://timmermade.com/product/alpha-direct-4004-overbag-2/

[Moab Randy]

I’ve used the Montbell Breeze Dry-Tec for several years. I think it must be the wide-long because it’s too big for me and I’ve thought about cutting it down. Oh well.

It does transfer moisture to a moderate degree, but not like the Goretex Pro in my kayaking drysuit. Not generally a problem as far as condensation; more of an issue of clammy in still air. Will not keep bag dry in heavy dew situations, and not because of leakage (but then I’m guessing any fabric would have the same problem).

It does extend the temperature rating of my bag and allows me to use my bag like a quilt (as I almost always do) down to lower temperatures. Theoretically it would allow me to carry a lighter bag. I also like having it as a reserve to keep the bag dry in blowing rain under my tarptent. I just keep my bag in the bivvy fulltime (protects it from leaking pack cover), and I put my pad under the bivvy.

But what I most particularly like about it is its utility in wind (and mosquitoes) when I sleep tentless, which is most of the time, especially if that wind is not cold–without the bivy, I’d have to be bundled up in a zipped down bag to avoid the wind, and that can be miserable. The bivvy is also useful for keeping gear dry, out of the blowing sand, or from getting lost, e.g., pants. (keeping water bottles from freezing?)

One thing I cannot endorse is using it in rain instead of a tent (except in emergency). Pretty miserable to feel that cold water accumulating just on the outside of that thin fabric, and it will get clammy in there (and how do you break camp in that scenario?). True with any bivvy, I imagine.

I strongly recommend you avoid all bivvy designs that use coated non-“breathable” fabrics on the “bottom”; an hour or two into your sleep and that “bottom” is just as likely to be on top, collecting condensation. I’ve built some that way and they are near-useless.

But I do like the very simple design of the MB bivvy–no zipper needed, just a big opening with a drawstring. I use it upside down. When it gets windy or real cold, the “hood” can just flop over me while still venting underneath as needed. That’s the way I also use all my sleeping bags (I have VB liners sewn into my bags). When it’s cold, keeping in that energy-packed exhalation goes a long way to keeping me warm. Never could understand why everyone wants to lose all that good heat, and get more sore throats in the night from cold air sucking out moisture.

 

[J-L]

Never could understand why everyone wants to lose all that good heat, and get more sore throats in the night from cold air sucking out moisture.

Timmermade’s Waterbear hood has made a huge impact on my cold weather sleeping comfort. It’s so nice having a warm face, and it helps with dry throat as well.

[Moab Randy]

Thanks for the tip, John. Same concept, different approach with some advantages of its own. And amazing how much it does look like a waterbear (tardigrade), possibly the most durable of all creatures on earth (and now in space).

[Author]

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