Hello all you bivy makers. I need some advise on materials for a winter bivy. I am transitioning to tarp camping and would like to make a winter bivy. This will be used on winter trips to Canada under a tarp, with conditions ranging from 20 F to -40F. Fellow hikers that have taken this trip before say that a very breathable and very slippery fabric is needed for the top and a waterproof fabric for the bottom. It will be oversized to fit me with my layers and botties and sleeping bag. (also any pieces of clothing that need to be dried out by the body heat method) I'm not sure if the ccf pad goes in or out of the bivy.

Top - momentum ?

Bottom - Silnylon ?

Thanks again for all of the help that the members of this forum have given me.

Dave

Dave,

I definitely recommend that you build your bivy large enough to fit your pad for winter use. Much warmer to keep the pad out of the weather. You can check out my bivy sacks for some ideas. I generate a lot of condensation, so finding a fully waterproof fabric with high breathability was my first priority. I'm 6'2" and 250 lbs so roomy was also important. Being able to get dressed inside the bivy is very nice. I've made a lot of prototypes getting here so I would be glad to help you avoid some of my mistakes :)

http://www.milesgear.com/

Dave

I keep the CCF pad outside, and take the inflatable (A Multimat torso length) pad inside. This works well for me till -36°C and I find there's no difference in warmth with the CCF pad inside or outside; though with the CCF pad outside it is easier to set up, and protect the bottom of the bivy. With this configuration one also doesn't necessarily need to use a waterproof material on the bottom, but can build in one material.

I long have been an advocate of tyvek for bivys. Especially for winter it is the best material, as it is the most breathable. I found Epic not very breathable at all, building up a lot of condensation, and also eVent and Pertex are not as breathable (all my subjective experiences). A further advantage of tyvek is that it is easy to get and affordable, and also easier to work with that e.g. silnylon.

"though with the CCF pad outside it is easier to set up, and protect the bottom of the bivy. With this configuration one also doesn't necessarily need to use a waterproof material on the bottom, but can build in one material."

I'm a bit biased to even talk on this issue since I would not use a bivy in the winter, but I just had to ask: Why the non-waterproof material makes a difference either way if you put pad inside the bivy? Moisture shouldn't come through the CCF pad anyway. Actually waterproof bottom sounds more important when you are using CCF outside, as the wind could bring snow between your bivy and CCF.

Thanks for your replies. I appreciate being able to learn from another’s trials. I had read about the limited breathability of the expensive “super" fabrics. I did not realize that tyvek is breathable. I have always used it for ground cloths.
There are many grades of tyvek available, which do you use? I have used house wrap and it was stiff and noisy.

Dave: I am very impressed with your bivy and I don't wish to impede your business venture by asking for your secrets. If you don't wish to share I will understand. What is the short name for your top fabric and is it available for the lay person to order? If no, could I order it from you ? Do you sew tyvek, how do you seal the seams? The design I am envisioning is basically a sleep system wrap. I am using a tarp, so I don’t need the full protection of a bombproof bivy. I need it to contain my sleep system and keep spindrift off and breathe like crazy. In the cold mornings, I want to be able to shift around and cook while still in my bag.( may need an integral ground sheet around the head area for tasks) I will wearing my boot liners and storing water bottles, extra layers in/on my bag for warmth. I would only emerge from my cocoon once it is time to put on the muks and pack the sled. I would then roll-up the system and stuff it into a compression sack (there may need to be some sort off attachment system of the bag to the sack) The more tasks you can do while wearing all of your glove layers - the better off your fingers will be.

Hendrik: Thanks for your advice about the fabrics and ccf pad. I use a neoair and will leave it in the bag and use the ccf outside. I also use the ccf on top of my gear in the sled for protection. This would also allow me to roll up my sleeping system as stated above.


Thanks,

Dave

A bivy is a very viable tool in winter use. I question if it is smart to not use a bivy in winter, be it in a snow cave, tarp or tent.

Non-waterproof (or not 100% waterproof, keeping in mind that no material really is - except maybe a plastic bag) because the more breathable material around you, the better. Indeed there's no moisture coming through the pad. The snow which might be blown to the side of the bivy & CCF pad is in my experience minimal, and does not pose a risk of wetting through - tyvek has a bit of waterproofness, which is sufficient for dealing with spindrift and drizzle.

"There are many grades of tyvek available, which do you use? I have used house wrap and it was stiff and noisy."

As I purchased my tyvek bivy from Laufbursche I can not tell you which exact tyvek was used. It is fairly light (205 gram for a 220 cm long bivy with a mesh window) and soft to the touch. Maybe you should ask him or some of the others here, which tyvek is good for this purpose. IIRC he even posted a guide here about that bivy...

Dave: I don't mind sharing my secrets since I have been a MYOG person for 30+ years and like to encourage others to try out their ideas. I would have just bought my Uber Bivy if someone else was making it. But as usual with MYOG projects, I make them because I can't find just what I need. Most of my rescues are above treeline and in high winds so a bivy is my best choice. Your logic of getting everything done while in the bivy is also my plan. I like to get ready to face the elements while still protected (especially from spindrift).

I sized mine to fit my 25" wide NeoAir but I would not recommend a NeoAir for winter (except for the new all-season NeoAir). I have been using Tyvek HomeWrap for the bottom and it is much more waterproof than breathable. If I use it on top there is lots of condensation. I do everything I can to avoid getting wet, especially in the winter. I also went with Tyvek to protect my NeoAir from puncture.

The fabric on top is not available from the maker by the yard, but I would be willing to sell small amounts to MYOG builders. Did you have a particular plan in mind yet?

Dave

Great discussion folks. David Miles is the "polypropylene microporous membrane" the same material as Dri Ducks?

I am with you all on getting as much done, still in the bag, as possible and then hitting the trail when ready just after pulling the legs out and putting the boots on.

I will add this thread to my Bivy Condensation piece reference section too. Thanks.

Thanks for all of the replies.

Dave: Once tyvek was mentioned as a viable material, I did a site search and found reams of material. I haven’t read it all yet, but I do think that a good pattern would be a cross between your uber bivy and this sleeping bag sack.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=46661

I would add an oversized rectangular piece at the head. For fiddling with gear in and maybe add straps to roll the entire setup into a compressible tubular size-or - It may be possible to just use a ground cloth and bond the sides to it and add a top. This way I could roll it up easier. I have three elongated side compression stuff sacks that I use in my sled - one for my "fat" suit, another for my sleeping system/tarp and the third for misc. gear. The foot area will need to be enlarged and squared off as I sleep in my felt liners and sometimes have a heated water bottle for comfort. Where we hike is in the woods and usually on top of three feet of snow - puncture resistance is usually not an issue.

I greatly appreciate the offer to sell me the materials. I will e-mail you from your site when I settle on a plan.

Thanks everyone,

Dave

Alex: This material is similar to Dri Ducks but made in the U.S. instead of China. I have a few Dri Ducks ponchos that I originally planed to cut up and make my bivy. They tear far easier than I wanted. I will just keep them as backup ponchos for the kids. I will read you Bivy Condensation piece later today. My experience with my GoreTex bivy sacks is what led me to find this top fabric. It is far more breathable than my GoreTex and still waterproof.

Dave: The pattern on the link you gave looks like a clasic style but has a few problems. First the zipper is nice for entry but has no protection from rain. It's not even a water resistant zipper. It also does not have a cover for the head area. Nice for bugs though. Take a look at my basic bivy. I'm going to change this to have a Tyvek bottom, but the simple drawstring opening can be positioned above, below, or to the side. The idea was for a simple winter bag when bugs are not an issue. I used one in February to rescue an skier who had been lost for 2 nights. I have also made a simple top with a closure like a simple sandwich bag. Very simple and weatherproof.

Dave

"A bivy is a very viable tool in winter use. I question if it is smart to not use a bivy in winter, be it in a snow cave, tarp or tent. "

Probably, but it's just that I have managed to get along to this age in all of those sleeping setups you mention without a bivy and it's against my lightening principle to add weight to my setup if I can live without.

But it was not the point in my question and reasoning - let's forget it since we are apparently speaking about the same thing, just from different point of view. I agree that more breathing on all sides is better - but I also think that more breathing on all sides is better with CCF inside the bivy too.

A few more thoughts:

Alex: I read your piece and I have traveled a similar path. The fabric I'm using has a soft fuzzy feel on the inside that I think helps to wick the moisture out. Also at the molecular level, many W/B fabrics have a monolithic membrane that the vapor has to get through. This adds another cooling effect which aggravates the condensation problem. Where do you live and would you like to beta test a bag for me?

Dave: I sew the materials together using heavy polyester thread and then seam seal using and irrigation syringe and Seam Grip. I would like to see some plans when you get closer. Ditto on the beta test.

Another good way to reduce condensation.......cram 2 people ("heaters") in the bivy :)

See my last entry on the following thread.
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=43910

Dave

Its probaly 1443 that's what I made my bivy with got it off amazon

Dave,

I don't think it has to be much more complicated than your basic bivy. It may be just as easy to modify it. I don't need any zippers, unless you can figure out a way to put a zipper in a certain place so I don't have to get up and pee in the middle of the night. It would be nice to cinch the head down at night, but fold it back out of the way for breakfast and early morning chores ( sandwich bag style). It would need an oversized - ground cloth looking piece that would only be attached near the waist and run up past the head. This would serve as a working area and the final cinch area when I roll the entire bivy/sleeping bag/deflated neoair up into a tube for travel.

I'll work more on the concept and a few crude drawings this weekend during downtime on our cold case SAR.

Thanks,

Dave

P.S. When I searched winter bivy I got few results. I search tyvek bivy and get 5 pages, but not your uber bivy. go figure.

Dave,

I spent a night in my basic bivy last February when it was about 10° F. It's quite large which makes it very easy to get in and out. It also gives me lots of room for clothes and gear. I like being able to adjust the size and position of the opening for cooking outside or sleeping on my side. By making the opening small and tucking it under my head, I can completely seal the bag from the elements. I like the no zippers, since protecting them can be a design challenge. As for relief during the night we use a pee bottle so we don't have to get out.

I'll be doing SAR work this weekend also. We are testing a team for entry into the MRA.

I'm not surprised by you search results since I have not done a very good job of optimizing my web pages for the search engines.

Look forward to your drawings. I'll try to get some pics of my sandwich bag opening.

Dave

After a two day basecamp (sleeping in a mid style shelter) my Tyvek ground sheet was frozen into the snow and had to be peeled off when we packed up to leave. It ripped and left a good amount of itself behind. Has anyone else experienced this. It makes me wary of using Tyvek as a bivy bottom.

I have had a similar problem when using Tyvek booties as "camp muluks." It seemed like a great idea at the time: foam hotel slippers + down socks + oversized Tyvek booties = 4 oz. winter camp shoes. Unfortunately, I found that the snow would stick to the bottom and sides of the tyvek and was very difficult to remove to the point of the fabric being useless after one night of use. Ironically, this helped provide traction, but otherwise, they were a pain to even clean sufficiently to pack out as garbage. As an aside, the rest of the system worked great.

Lynn,

I use a tyvek bivy by Laufburche that I combine with a tyvek duomid knock-off and have not experience the problem you described. Snow has stuck to both the shelter and the bivy but I just packed it up lightly brushing off as much as possible before stuffing it into my pack. With any material frozen to the ground, which sounds somewhat similar to the condition you described, care must be taken with trying to remove it without damaging the material. Tyvek is a tad more fragile than more commonly used material and requires more care. The bivy is pefect for what i use it for mainly for the high breathability and the protection from moisture due to blowing snow or rain spray.

Thanks John, It is true that I was unaware of the fragility of Tyvek, though I would like to think I was trying to peel it out pretty carefully.

In retrospect I should not have left it under the tarp all day in the warm Spring Sierra sun. It wasn't frozen to the snow it was frozen IN the snow. Maybe it absorbed quite a bit of water during the day? My ski buddies coated nylon groundsheet didn't become one with the snow like the Tyvek did.

Just curious which type of Tyvek was being used. Was it HomeWrap or soft structure? It sounds like this is a problem of warm days melting the snow into a puddle and then refreezing at night. I'm usually packed up in the morning while still sub-freezing. I'm going to perform some tests and see what it does.