Designing a couple of Bivy sacks

Hi, happy to help you out – need beta testing eh?

I think there are two (or three) basic backpacking bivys

1. UL Bag Cover and Net – provides protection for the sleeping bag w/wo tarp, netting provides enough space to read in the bag away from bugs. Netting could be supported by a pole – or preferably can be hung from a tarp/pole
My fave here is the MD Sleeping Bag Cover – w/ a clip-up head net it could be great

2. climbers bivy – heavier, U-zip, clip/tie in. WT eVent Bivy is I think the best version of this – the zip in netting is poorly done and could use more structure.

3. full on bivy tent

4. simple sleeping bag cover – ie. MB Sleeping Bag Cover

IMO if I were you I would be looking to design the two bivys for diffrent users, one a climbing bivy, two an UL bivy.

For the UL Bivy I would look at Silinylon floors, no side zip (weight) and a target weight of under 12oz.

I have never used the DriZone fabric and with eVent/Gore am not sure what the incentive is?

I usually have a tarp of some kind when bivying (even in the Alpine). For Backpacking I want my bivy to create a roomyish spot to sleep and read protected from bugs. It also needs to protect the part of my sleeping bag that sticks out from the tarp from rain.

Here's what I want in a UL bivy.

• <10 ounces
• Silnylon floor with silicone stripes/dots to prevent slipping
• DWR top
• Short side zip
• Net hood. No need for a solid cover
• Tie outs. Some to anchor to the ground so it doesn't blow away, another for the hood to get it off the face.

If it only adds 1-2 ounces, allowing the top to zip down to about the waist to expose a netted surface might be nice. That would allow better ventilation on warmer nights while still providing bug protection.

I'll also volunteer to be a beta tester! I just got a new SD Wu Hu tent delivered yesterday. ;)

If we're talking "blue sky", I think the weight goals should be more aggressive. A simple bivy with a silnylon bottom, lightweight DWR top and bug net hood should come in around 6-8 ounces. I would love to see something with M50 or a comparable material on top.

"For the UL Bivy I would look at Silinylon floors, no side zip (weight) and a target weight of under 12oz."

Good grief! I sewed my own with one chest zipper, one side zipper, and it came out a hair over 8 ounces.

–B.G.–

I have to add a vote for a minimalist bug bivy. A waterproof non slip floor, waterproof/resistant foot box for any splashes or rain that could enter under a tarp then mesh from mid shin or knee up to ensure some breathability, a vertical zip from chin to belly button, tie outs and all at around 8 oz. I'm not sure how tall of an order that is but you creative types never fail to impress!

If we're talking "blue sky", I think the weight goals should be more aggressive. A simple bivy with a silnylon bottom, lightweight DWR top and bug net hood should come in around 6-8 ounces. I would love to see something with M50 or a comparable material on top.

Sure, that'd be nice too. Go with 20D silnylon, or even more aggressive, a cuben fiber floor. M50 top is about as light as it gets. Still though, Sierra Designs isn't known for having the lightest equipment. I think it'd be good if it was well made, good looking, and have a couple nice extra features to make it an easier transition to UL.

I am not sure what can be brought to the table unless a mass produced bivy/small net "tent" can be made for less and still weigh at or around the cottage gear makers. With a constraint of having to used fire resistant fabrics, I don't know if this can even be accomplished.

I have been impressed with Golite's Sil/PU coated fabric in the 2010 and later tarps, but I don't know if it would meet the fire retardant standard for a bivy. That would meet the UL weight requirement and would all but eliminate the pad slip associated with a silnylon fabric only. That type of floor fabric with a half zip and partial nanomesh and highly breathable DWR top in the 1.0z or less per sq yard category would certainly work. Make another just the same but with a full solid DWR UL top and mesh over the face, and bring them to market at $99.95/$119.95 respectively list price and you may sell quite a few, but perhaps not enough to justify mass production. Target weights would have to be in the 8 – 10oz range, which is some 10-20% higher than the best of the cottage gear, but at a lower price you could still remain competitive.

You've pretty much summed up the scenario… My hope right now is to explore these options and see what is viable to produce. Mainstream industry confuses "ultralight" with "lightweight" when it comes to products. I would like to create an option geared specifically to the UL crowd by possibly offering a bivy/tarp combo. Materials and appearance would tie them together, but wouldn't necessarily have to be used that way. That could turn into a solo-tent instead.

Great ideas everyone and I truly appreciate the feedback.

FR will be required…

…but not in the prototypes;)

Hi Austin,

I would like to see this bivy made in the USA.

Me too!

For a moment I thought you meant the bivy/tarp combo would be one piece of gear and I was thinking that the condensation inside would be horrendous. Oops. I like the idea of matching pieces of gear. There's some very well made ultralight gear, but it often makes us look like crazy hobos to the unwashed…like ski pole carrying freaks in sneakers with packs made out of grocery bags! So I imagine that it will attract more users if the gear looked like it was actually worth something.

>Keeping in mind the limitations of cost, fabric availability and legal requirements (i.e. FR)

These criteria are going to be problematic if you try to replicate what people in this thread (including me) tell you is the ideal bivy. Also, a lot of the weights people are telling you to shoot for are too heavy. 8 ounces is my upper limit for the type of bivy meant to be used with a tarp.

I sewed my own bivy years ago out of silnylon (bottom), dwr nylon (top of bivy up to the shoulders) and bug netting (top of bivy over head), made it big enough for a 6' man + 20 degree down bag, and it only weighs 5.6 ounces. The zipper (which is pretty long) is down the middle, so I can sit up in it while unzipped while keeping the silnylon squarely between me and potentially wet ground.

The purpose of my bivy is really simple. It has to work as a component with a tarp to 1) keep rain spray and dew off my sleeping bag, and 2) provide a bug- and snake-free refuge for me to sleep in, necessary in certain environments for peace of mind. Since neither of those things are necessary in UL backpacking, I don't want to carry a lot of weight for it. I would not carry a bivy that's not intended to be my primary shelter if it were over 8 ounces.

If I were to make it again, I would make the foot-end more waterproof. I rarely have any problems with getting my sleeping bag wet because my tarp is really big, but if the foot of my bivy touches a wet tarp, it's only a matter of time before it wets out. A WP/B fabric, or at least a more waterproof DWR fabric down there would be better. Golite has the right idea in a lot of their quilts and sleeping bags.

Austin,

I would love to see more girth at the top of the bag. I like when I can pull them over my 6'2" frame. I took the zipper off of my current one and use it like a quilt. When the weather is bad I tuck it up under me and have had no problems. The one I have uses a little more fabric but works great. It is more of a fold over closure. It allows me to air it out a few times at night, also.

Either this or a center zipper down to the waste, witha bug mesh gusset down the middle.

Thanks.

for me

under 10 oz

side zip for sure

mesh hood area with tie out loop

must accomidate a neo air or big agnes air core pad plus sleeping bag plus myself inside without compressing the bag

waterproof taped seam floor with breathable top

less than $150 some of us are not made of money lol

kevin

Austin, please refresh my memory re FR requirements…are there any? Whose are they…Sierra Designs in house, industry standard, what?
Thanks,
Steve

Kevin, you are so spot on!
+1 from me.

Bag length should easily be able to accommodate someone well over 6'. Too often, both in tents and bivy sacks, they are designed to fit someone <5'10" so that the published marketing weight can be lowered.

For the taller folk amongst us, we know the gear may cost slightly more in dollars and weight, but it doesn't do any good if the max bivy length is 80 or 84"; a sleeping bag ends up compressed at both feet and head.

I'd seriously consider a UL bag bivy with an eVent top. In snow caves & igloos condensation inside the top can be a problem but I'd bet that eVent, with its better and more direct breathability, will reduce it a lot.

The silnylon floor is still likely the best idea for a UL bivy. But "no zippers" seems much too inconveniant so perhaps a high quality, smaller half zippoer should be considered.

+2 with Kevin.

re: kevin,
>mesh hood area with tie out loop
>waterproof taped seam floor with breathable top

A sheet of silnylon is big enough that you can easily make a bivy bottom out of a single piece. If the top is made of mesh and "breathable" (I assume you mean DWR nylon?) then what's the point of taping the seams? Or are you talking about a free-standing bivy?

We have made some bathtub groundsheets as well as a couple bivies using 30d sil and a DWR top.

I prefer a screen face area period. The only way I would not is if I'm only carrying the bivy which I don't do for anything practical. I prefer slightly big sizing, since so many things are made for people on the small side, the weight difference is so minimal. The bivy gives some peace of mind in snake country, as well for the family at least it helps keep gear cleaner. The side zip in my mind is worth it's weight period even if it was a number 10 zipper :). A peace of gear needs to function easily to get used, if it doesn't function easily then it doesn't get used much.

6 – 8 ounces should be doable as that is close to what our prototypes came in at.

We have toyed with the idea of double bivies as well, especially for the kids as a weight saver. Traveling as a family, we can save a lot of weight by using a double bivy + a double quilt over singles.

A sheet of silnylon is big enough that you can easily make a bivy bottom out of a single piece. If the top is made of mesh and "breathable" (I assume you mean DWR nylon?) then what's the point of taping the seams? Or are you talking about a free-standing bivy?

if only the hood area is mesh and the rest of the TOP is breathable material there is a seam where the floor and top material are sewn together right?? ok that seam may or may not be high enough up the side of the floor depending on how big the floor material is to prevent water from getting in the seam even if it is high enough it will still leak when you roll on your side and the bivy goes with you so now the seam is on the wet ground andleaking on your 850 fill down bag

not my idea of fun but keep in mind its only my opinion and how I would want mine to be done :)

kevin

OK, so what I'm getting at is if you roll a silnylon/DWR nylon bivy on its side on wet ground, the DWR will wet out and soak water through your sleeping bag anyway, so what's the point of taping the seams, when, if done right (i.e. some sort of folding/double-stitching), the seams aren't exactly water siphons in the first place. There are people who never seam-seal the ridgelines of their tarps and don't have serious issues with rain coming through. Then again, you also have the issue of silnylon having a low enough hydrostatic head that if you threw it over a puddle, and then laid on it for the night, you could reasonably expect leakage even if you'd taped, glued, and heat-treated all the seams.

IMO, many people who look at pictures of bivy sacks and read descriptions of their features tend to visualize them as though they were miniature tents. They are not. A bathtub floor is completely nonfunctional when there is no tension holding the thing up. Silnylon is highly waterproof, but has cruddy durability. Rub it on a sharp rock at the wrong angle, and it will get a water-permeable hole.

What I usually do, when camping with a tarp + dwr bivy, is first find a good site that won't puddle water in a storm, and second, use my polycro groundcloth for any moisture that comes up from the ground overnight. The groundcloth weighs about an ounce and a half and is essential if I want a dry and clean space to set my gear when tarp camping, in case the ground is already a little muddy. So I'm bringing it anyway, but this small addition also takes care of all the problems enumerated in the first two paragraphs, and is the reason why my upper limit for dwr bivy weight is 8 ounces.