Forum Index » General Lightweight Backpacking Discussion » Bivy sacks and increased warmth?


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Chad Miller
(chadnsc)

Locale: Duluth, Minnesota
Bivy sacks and increased warmth? on 10/26/2007 09:26:20 MDT Print View

Well I just picker up an Integral Designs Micro Bivy and I love it!

I was wondering how much added warmth I could expect to gain from using the bivy. I’ve heard a wide range of information from 5-15 degrees.

Thanks for your help!

Edited by chadnsc on 10/26/2007 09:26:59 MDT.

John Mowery
(Mow) - F - M

Locale: Minnesota, USA
Increased Warmth on 10/29/2007 08:39:19 MDT Print View

I was paging through the Hilleberg catalog last night and it cited a European government testing body as verifying a 7 degree Fahrenheit increase in sleeping bag comfort when used in combination with a bivy.

Sam Haraldson
(sharalds) - MLife

Locale: Gallatin Range
Re: Bivy sacks and increased warmth? on 10/29/2007 09:55:03 MDT Print View

Chad -

As you know temperature ratings on sleeping gear vary because of the dynamics of human physiology so I'm not going to give you a line of B.S. about how much warmer it will keep you.

I presume you're asking this in terms of winter trips up on the shore, yes? The ID Micro Bivy being a minimal shelter of eVent fabric is going to do good things in terms of keeping wind out of your bag/quilt combo which will significantly cut down on windchill.

This is a bit off topic, but you may encounter issues with the breathability of the eVent when temperatures drop below zero. Perspiration exiting the pores of the fabric can freeze creating an impenetrable barrier thereby causing condensation within the bivy. A good solution to this would be a next-to-skin vapor barrier system keeping the perspiration next to your body and not collecting in your bag's insulation. Search BPL for myriad quality discussions of vapor barrier.

- Sam

Chad Miller
(chadnsc)

Locale: Duluth, Minnesota
VB and bivies on 10/29/2007 10:44:49 MDT Print View

Thanks for the input!

I plan on using VB clothing for my winter trips.

Jason Brinkman
(jbrinkmanboi) - MLife

Locale: Idaho
Re: Bivy sacks and increased warmth? on 10/29/2007 13:25:33 MDT Print View

The answer is complicated and probably inconclusive due to the number of variables. I am not an expert on this, so anyone please correct anything misstated here.

The bivy should trap an additional non-uniform sized layer of air (conductive/radiative heat loss reduction?), and cut down on felt wind (convective heat loss reduction?), while possibly retarding the loss of moisture (evaporative heat loss reduction) although not losing moisture is not good in a sleep system.

Besides keeping you dry, the convective gain (blocking the wind) is probably the greatest warmth advantage to a bivy. But bear in mind that is only works when there is wind ~ thus the complexity of the answer. As others noted, if the bivy forms a sheet of ice, there will be no further evaporation, but the trapped moisture will wet your insulation, possibly leading to a collapse.

My rule of thumb for the purposes of my calculations is that my eVent bivy adds around 5 degrees Fahrenheit. But it's real advantage is in what it prevents me from losing. That is, my 30 degree sleeping bag would probably not feel like 30 degrees if used unprotected in a high wind.

Edited by jbrinkmanboi on 10/29/2007 15:14:27 MDT.

Paul Tree
(Paul_Tree) - F

Locale: Wowwww
Chad - what sleeping bag? on 10/29/2007 14:58:30 MDT Print View

Hey Chad, glad you love the new bivy - what sleeping bag do you use and how is the fit? How big are you?

In a snug bivy, how is condensation dealt with?

For instance with goggles, roomier = less easily fogged, so you'd think bigger the better...

Is it wicking condensation off better because it's closer to the heat source?

What temps have you had it at and what is the fabric of your sleeping bag?

Chad Miller
(chadnsc)

Locale: Duluth, Minnesota
my sleeping system on 10/30/2007 11:56:25 MDT Print View

Right now I'm using the following;

Integral Designs Micro Bivy
MontBell UL Down Hugger #3, long
MontBell warm-up sheet
Thermarest prolight 3 short sleeping pad

Eventually I'll pick up a MontBell UL Down Hugger #2 and possible an Nosnivler (sp?) quilt. I will soon be converting to the thermarest prolight 4 large pad for the colder temps.

As I'm shure Sam can attest to I'm a bigger guy, 6'3, 230 pounds with broad shoulders. I found the bivy to have plenty of room for me, my sleeping bag, pad, warm up sheet and fleece. In fact I have almost enough room to sit cross legged in my bivy. I've been in tempratures down to 25 degrees so far without feeling cold or having any condensation problems.

Matt Ahonen
(ahonenma) - F

Locale: Western MN
North Shore on 10/30/2007 15:19:00 MDT Print View

Chad -

This is off topic, but is Mike your dad?

Matt Ahonen
Moorhead, MN

Chad Miller
(chadnsc)

Locale: Duluth, Minnesota
off topic on 10/31/2007 07:37:34 MDT Print View

Yup, my dad's name is Mike. Their are a few Mike's in Moorhead though so you may need to be a bit more specific

Matt Ahonen
(ahonenma) - F

Locale: Western MN
Off Topic on 10/31/2007 08:59:40 MDT Print View

I should have just asked you if you graduated from MHS around 1994.

I graduated in 1993 and am good friends with Mike Manger.
It looks like he will be moving to Duluth shortly.

I was really surprised to see someone I know on the forum.
I an interested in doing some hiking on the SHT. Any info you could share about some of your favorite sections would be great.

mattahonen at hotmail

Thanks,
Matt

Sam Haraldson
(sharalds) - MLife

Locale: Gallatin Range
Bivy sacks and increased warmth? on 10/31/2007 10:18:00 MDT Print View

Matt -

I (and I presume Chad as well) highly suggest walking the SHT in it's entirety.

- Sam

Matt Ahonen
(ahonenma) - F

Locale: Western MN
Bivy Sacks on 10/31/2007 11:18:09 MDT Print View

I did the Devil's Track loop two winters ago, and we had a great trip.

I recently did a 3 day 60 mile hike from Hwy 64 to Itasca and through Itasca to Chimney road on the North Country Trail. Day 2 was almost entirely road walks and was a real grind, but it was my first trip with light gear, solo and high mileage.

Great experience, but wouldn't recommend it unless trying to complete NCT. The trail itself was great. Hopefully over the next couple of years additional trail will be added to cut out the road walk.

Looking forward to getting in some miles on the SHT.

Jim Colten
(jcolten)

Locale: MN
Re: Off Topic on 10/31/2007 11:35:12 MDT Print View

Matt,

There are only one or two sections of the SHT that I don't care to repeat but if you want to start with the best, my votes would be Silver Bay to Caribou River (45 miles) or Lutsen to Cascade River and then up the east side of the river to the next road (20 miles).