I see a lot of posts where people advocate adding a bivy for extra warmth in a breezy tarptent.

Wouldn't adding a 6 ounces of down to the bag/quilt be warmer than adding the bivy (and the same total weight) ?

Would adding 12 extra inches of width to the quilt block drafts that happen when the sleeper turns over about as well as the bivy ?

Also, are bivy's with nylon tops still prone to interior condensation ?

Thanks.

John,

You make well reasoned points, ones that Ray Jardine also promotes. In normal conditions I think either of those alternatives make sense. After all, 6oz of down is a lot of added warmth!

For me, the problem has more to do with wind blocking than insulation. I've been colder in high wind wearing thick fleece pants, and warmer when I switched to thin summer pants plus rain pants. And even though sleeping bags often use wind-resistant fabrics, there is something about cold, blowing air directly circulating around a thicker sleeping bag that is colder for me than having that extra layer of fabric (the bivy) on a less thick sleeping bag. As a quilt user, a bivy really helps as well.

I use a bivy for other reasons too, though. It's an added barrier to bowing rain and dripping condensation, and it lets me sleep under the stars when conditions permit while knowing I have a shelter to crawl into if I needed one.

I live in pretty rainy conditions, so I use a 2-layer wp/b bivy which gives me the peace of mind that, if stuck in a storm, I've got an emergency bivy. But I tend to hike in conditions where a double-wall tent may make more sense, so a bivy in a tarptent is a lightweight way for me to achieve similar results, and benefit from a wider range of comfortable conditions.

As always, I think one has to evaluate one's expected hiking conditions and how many safety nets one wants to put between ones self and hypothermia.

Edited by jcarter1 on 01/01/2009 19:32:50 MST.

I just did this last night. The wind blocking is a very nice benefit.

For me it's also an economic choice, thinking about my gear as a system. In the mostly warm-ish Georgia mountains, I get more use out of a tarptent and a bivy. The tarptent can go 3 seasons, plus fair winter weather. The bivy can do the same alone, with tarp, or with tarptent. I get more flexibility to mix and match.

A more heavily insulated bag or a more substantial/sealable tent are probably better gear choices for particular situations, but their functional range wouldn't be as wide and they wouldn't get as much use in my regular hiking climate.

-Mark

One last comment: I guess I see tarptents as more tarp than tent. When you think of tarping, you think of a bivy being required. Well, add mosquito netting and sewn-in groundsheet and you get a tarptent, not a double-wall shelter. Just because a tarptent is fully enclosed doesn't mean you are protected from the same problems tarp users face: blowing rain, dripping condensation, and breezes. Thus I still find a bivy as part of the overall system. But again, this is due to the conditions I may encounter in the area I hike in.

I use a tarptent for the bug protection in warm weather, and the bivy for the higher altitude camps. Since most of my hikes involve a little bit of both, I bring both.

I came to the same conclusion.

After doing the last 165 miles of the JMT in 2008 (last week of July, 1st week of August), in a tarptent (Squall Classic by Gossamer Gear) and a 32F Summerlite WM bag, in which I wore my WM Flight Jacket as well when it got extra cold during the night, I got cold at my legs and would have appreciated the extra warmth a bivy brings. I just ordered the Mountain Laurel Designs' Large Superlight Bivy (6.9 oz) at http://tinyurl.com/9ekaha . I figure this plus the above will keep me warm when I do the entire JMT in 2009. I could bring a 20F WM bag but that weighs 10 oz more and I figure the advantage of the Large Bivy is that I can slip my sleeping pad and bag in it, protecting the bottom of the pad from punctures and preventing me from rolling off of the pad during the night, giving me a more comfortable sleep too (all the while saving 3 oz over using a 10 oz heavier bag). I got the large because I may end up getting a Thermarest NeoAir pad which is 5'6" long, 20" wide, and 2.5" thick and for that extra thickness, I was told I needed the larger bivy (which only weighs .5 oz more). The NeoAir pad will save me 4 oz over my existing 17 oz 5' Montbell (1" thick) pad and be more comfortable too. See http://www.montbell.us/products/disp.php?cat_id=33&p_id=1124273 .

Roleigh,
The last I heard was that the NeoAir was due in April. Have you any information on the release date? I can hardly wait. The 66" is said to weigh 10 ounces.

Dennis, nothing new on my end but my memory showed the 66" one at 13 oz not 10 oz.

http://www.trailspace.com/blog/2008/08/09/therm-a-rest-neoair.html

"It will be available in April 2009 in four sizes, ranging in price from $120 to $170.

Small: 20 x 47 in. (51 x 119 cm), 9 oz. (260 g)
Medium: 20 x 66 in. (51 x 168 cm), 13 oz. (370 g)
Regular: 20 x 72 in. (51 x 183 cm), 14 oz. (410 g)
Large: 25 x 77 in. (63 x 196 cm), 1 lb. 3 oz. (550 g)
"

John G.,

I do exactly as you suggest: I put more weight in my sleeping bag and never use a bivy in a tarptent. 6 ounces of extra down in a sleeping bag gives far more warmth than any 6 ounce bivy can. I've also found most of the bivies that I've used tend towards condensation within the bivy so my sleeping bag gets wet anyway. I prefer a light pack towel to dry off any condensation that forms in my tarptent. If it is breezy then the wind is going to keep condensation down, so the real question is added warmth in the breeze. In my experience added down in the bag gives more warmth than added fabric from a bivy.

If really heavy continuous rain is forecast and it is a relatively short trip then I prefer to use a double wall tent. If I'm long-distance hiking for several continuous weeks then I'll go with a tarptent, warmer sleeping bag, a pack towel--and no bivy.

"I do exactly as you suggest: I put more weight in my sleeping bag and never use a bivy in a tarptent. 6 ounces of extra down in a sleeping bag gives far more warmth than any 6 ounce bivy can."

Unless the wind is blowing really hard - down does very poor against heat loss from Convection. Then a bivy will make much more sense (not including the warm micro-environment it creates. As much as 7 degrees).

Edited by FamilyGuy on 01/02/2009 12:08:13 MST.

The humidity is not that bad, typically, in the High Sierras (at least nothing like the Midwest). But the wind can be very strong sometimes if you are short of a pass. The bivy I bought reportedly has a very breathable top cover (not suitable for use without a tarp cover in rain), which is from Mountain Laurel Designs. I also do not need the bivy warmth for the upper body as I wear a Western Mountaineering Flight Jacket when it gets cold inside the sleeping bag. It is from the waist down that I need the extra warmth/protection from the wind. I am thinking condensation will not be an issue for me, as I ordered the bivy with a side zip down to the waist and I can have it unzipped most of the time. I'll find out if this is the best approach this July/August on the JMT and report back here.

I rarely get condensation using the equinox bivy, but do sometimes at the footbox.