View Full Version : MYOG/DIY Sleeping Bags
hallelujahjafar
09-09-2010, 19:25
Hey guys,
I'm curious about making my own bag rather than going out and spending 200-400 dollars for a Jacks-r-Better or a major brand bag. I know there is an endless amount of ideas within this MYOG forum, but I'm wanting to know what you guys might suggest to be the best. So if you have made your own bag or atleast know what some of the best designs are, please feel free to let me know what they are.
I've been think about this myself lately.
The science of heat loss when sleeping is pretty complicated. I've studied it in different ways, and experienced it in different ways, down to -20F to -30F a few times in the backyard, and I am still not that happy that the science is all that well understood. In particular, even with good designs, I think the heat loss from the neck and face and head regions is greatly underestimated, particularly in winter bags. This business of simply increasing the loft by an inch or so for every 10F or 20F is rather simplistic. At some point less heat is actually lost through the insulation, compared to heat lost through breathing, and from more exposed areas around the mouth, and from ventilation to the rest of the bag even if you have a good neck dam there. The head and neck doesn't vasoconstrict as well as the rest of the body either. I am not saying you don't need a thicker bag. I am just saying that at some point the thickness is just providing thermal mass, not insulation, for giving you some warmth back more quickly after some cold air rushes in somehow or other. A sleeping bag is rather like a house with the front door wide open, or just covered with a wool blanket. You still need thick walls, but at some point you are really getting diminishing returns on the insulation in the walls, and it is more the mass of the walls that gives you some comfort when some wind blows in through the front door.
So I would focus on some of those details, like a good neck dam to keep ventilation into and out of the bag to a minimum. There will always be some, and I really think wearing a thick wool sweater to bed on coldest nights helps alot because the air sort of flows through the wool sweater which acts as a sort of plug and it acts as a sort of heat recovery unit. The other thing is the neck and hood area needs to be very well insulated, and again I think it helps to wear a wool neck tube and balaclava in addition to the insulated hood. A separate insulated hood, like the finbar hood or jacks-r-better hood, either in addition to the sleeping bag hood or instead of the sleeping bag hood if really thick makes alot of sense. I am not sure what is best. On one hand I like the idea of being able to turn your head independantly. On the other hand I think it should be integrated. There are alot of conflicting interests. You also want to keep it simple, and minimize extra nylon weight at the expense of insulation weight, and you also want to minimize overall surface area. Although again, I think the ventilation losses are as important as the losses through the insulation, so its complicated. The other thing that is going on is evaporative losses, which are about 20% I think. Some of this is from your breath and some of this is from your skin. If the moisture from your skin is captured in wool underwear or your sweater it is recovered, as long as you can get it fully dry again while wearing it during the day. The breath moisture is more problematic. You really need to get rid of all of this moisture, but you can still use a wool neck tube or scarf as a heat exchanger. Your breath warms up the wet wool on the way out, melting the frost that has formed on and in the wool, and when you breath air back in the air is warmed as it recondenses and refreezes the moisture and water in and on the wool. There are some rather simple and skimpy balaclavas out there for this purpose, but they aren't scaled up for 0F to -30F. For that and colder I think you simply need thicker knit wool, but still lose enough to be able to breathe through. Also, you need to be able to adjust it easily depending on how cold it is and how warmed up you are and how much you are breathing. This is not so easy if your arms are stuck down in the sleeping bag under the neck dam and wool sweater. Sometimes you can sneak a hand up and sort things out and then tighten up the neck damn again. If there is a bivy sack or tent, and it has some adjustments also, that adds some dimensions. Last but not least is the ground pad situation. In theory, on snow you only need to insulate for 32F, as the snow acts as an insulator from that point onward. But what if it is hard packed, or if cold air gets under the pad, or if there is no snow, just -30F hard frozen ground or rock or ice. So how much weight should go into the bag and how much weight should go into the sleeping pad? I like the idea of assymetrical bags that have more insulation on top than underneath, and I think two 3/8" thick pads is usually enough, but on that -25F night in the backyard I think I was still losing too much through my back, though the compressed sleeping bag and the two 3/8" pads, perhaps because there was no snow and lumpy ground and so cold air was getting underneath. This caused me to move around, and that caused more ventilation into and out of the sleeping bag, and that caused me to shiver and increase my breathing some more, and get my hood and all that all messed up. A viscous cycle for sure, ultimately leading to me bailing out and heading inside my house. I did make it to 6am though.
or colder
, and this business of simply increasing the loft
I say start off with a synthetic quilt. Climashield according to what temp range.
If you want to make it really simple just build it squarish with a draw sting foot box and a short zip of velcro about 12- 18" long. No quilting required, just sew the edges.
2.5 oz, 3.7 oz 5 oz = roughly 45df, 35df, 25df +- 5-10 depending on how you sleep.
Perfect for a hammock which is super easy to build too.
I guess I am saying very little heat is lost through the insulation versus what is lost in other ways, like ventilation, respiration, through the bottom where the loft is reduced and cold air gets between the bag and the ground pad, or perhaps through the ground pad if it is thin and there is no snow or really cold air gets under the pad.
Extra loft doesn't weigh much, and is always a good thing, but does not make up for flaws in the design, or a poor fit, or lack of experience in knowing how to use the bag and clothing to stay warm and settled at extreme temperatures.
Anyhow, for 20-30F this is probably less important. Just about any decent bag or quilt should do. Wearing a wool neck tube and balaclava and perhaps an insulated hood can make the design and construction of a DIY quilt or bag alot easier though, for down to 20F.
hallelujahjafar
09-10-2010, 16:44
JAK--Thanks a lot for all of the tips. I'll be sure to keep those in mind when I begin to work on the bag. I'm not sure I'll ever be using this bag in temps down past 10F. In fact, I doubt I'll even get to where I'm in that low of a temp haha. I am basically wanting a 15F bag, but I am unsure how to start. I will keep some of the warmth loss tips in mind with the design though so thank you very much for those.
Tammons-- I've thought about using synthetic simply for the fact that it seems more simple to work with, but wouldn't going with down create a much lighter bag? I did find a site with fairly cheap down.
What would you guys suggest for the inner and outer shell? (I probably should know this, but I am unsure.)
Have you seen this site (http://thru-hiker.com/kits/)? Lots here to look at.
Down would be better all around, somewhat lighter, and more compressible, but its a real PIA to work with. I worked with down years ago and its a real mess.
You will do it one time.
The best way to work with it is in a tent or if you are a pro you will probably have a down room. People I have read of sew their shell, pu tit and the sewing machine inside a tent and fill and close the baffles inside the tent.
Tim Marshall who is a custom builder uses a wet vac to fill baffles.
From what I have figured out Climashield is about equal to 550-600 loft down.
To build a down quilt would not be too bad, but building a down mummy bag would be way too difficult for a first down project.
Even to build a real down quilt you have to build baffles, close the ends properly etc. fill the baffles.
With a rectangular climashield quilt you just sew the edges turn it inside out and close it up.
I used to always think the way to go on the shell was some simple light nylon, but now I am not so sure. If most of the heat loss is not through the insulation in the conventional sense, then maybe there is something else going on there, like actual ventilation through the inner and outer shells. A little might be ok to control moisture and keep the bag dry without being too wet and clammy inside, but how much airflow is there into and out of the bag through the shell? I'll bet there is some. Hot air in the bag will want to rise, so on a cold night I would bet there is considerable convection into and out of the bag through the outer shell. So you have less insulation when you need it the most. A bivy might take care of this. Not sure. I am not sure but an outer shell that frosts up a bit when it is really cold might not be a bad idea either. This would be just about any fabric I would think, so breathable nylon might be ok after all. I don't really know about lightweight windproof fabrics that allow vapour through. I know that my army gortex bivy works but it is very heavy at 2 pounds for about 2.85 square meters, so it would be 1.4 pounds for the outer shell of a sleeping bag. The inner shell could be a lightweight nylon I am pretty sure, but for a homemade bag you might consider using silk, or maybe even fleece or wool as the inner shell, and then not use a liner. You could turn it inside out to dry the inner shell if it was wool or fleece. I think wool has very useful properties for this purpose, having to do with heat recovery from water vapor leaving your skin. Fleece would just be cozy. Fleece and wool are heavy though, compared to light nylon or polyester. The omnidry nylon that columbia hiking shorts are made from would be comfortable, but perhaps too heavy. I have heard of pertex and quantum, but I don't know what they are in terms of material or how you would get some.
I think synthetic batt would be easier to work with than down, and for a 15F bag the baffling and construction would be alot easier. I am thinking of making a winter bag using my gortex bivy. The gortex bivy would be the outer shell, and removeable. So the synthetic batt would only have a shell attached on the inner surface. The inner shell might be nylon, or I might try something like wool. I think I will go with nylon so that a wool blanket or liner or long underwear could always be used anyway, or not used, depending on how cold it was, and the wool would be easier to dry out with the sleeping bag packed away. Rather than keep the bivy as a 80"x30" rectangle I am going to cut it down some to a tapered shape, more like a mummy but still flat and simple and roll-upable.
Bags4266
09-10-2010, 21:04
Go over to www.hammockforums.net (http://www.hammockforums.net) you will get many ideas on quilts synthetic and down. Also many vendors there who sell and help you as you go and ask questions. I have made 3 quilts of different weights of climashield insulation. What I found is you loose most of your warmth from moving around while sleeping when tenting. When I hammock I stay much warmer there is little ventilation.
Of course you can add flaps to your quilt, there are many sizes and styles to read about there and keep you busy for weeks.
hallelujahjafar
09-11-2010, 00:27
Thanks so much for the input guys. I'll be sure to check out both thru-hiker and hammock forum. As for the down issue, I agree with you guys in the most part about the difficulties of dealing with down. I guess I am simply concerned that if I make it with synthetic I'll end up with a bulking/not-so-light bag. I would experiment with ideas and everything, but I really just want to get one built and hope it lasts me for a while haha I'm sure its not a process you really want to go through many times and all unless you are just full of ideas. Once again, you guys are great. I'm glad to see that I can get such experienced responses through this site. Glad I found it haha.
Tim Marshall who is a custom builder uses a wet vac to fill baffles.
He does good work too. I got my cuben fiber down filled quilt from him. Great quilt. It would be even better if I got over my issue with bugs so I could get rid of my bivy.
You can build a 45-50d climasheild quilt of 1 oz nylon and the weight will be 12-14oz depending on the width and length. If you buy walmart 2nds nylon you could build one for about $40.
JAK's reply a half-decade ago is mostly true and experienced by myself as a kid (and by my young kids too) ... but here's the answer to your question of 'How to Sleep Warm Outside Cheap'
1. Make a $15 R10 sleeping pad from EPS foam (bought from Lowes or HD). See how-to at http://www.slideshare.net/sweerek/diy-sleeping-pad-eps-accordian-27mar15 . Then put a comfortable, summer, non-air, pad atop this warm but rigid base. Contrary to JAK, you'll lose ~ same heat down as up.
2. Use your existing summer bags as the base layer. If you've two such bags, use them both. (Walmart's $20 bags layered & fluffed up are a good value.)
3. Depending on how much room you have and travel means (car? sled?), bring polyester or down comforters and place over your bags (like a quilt). Fluffy pillows too. These can be bought cheaply at GoodWill / thrift stores. Since these are cotton, consider how you'll keep them dry.
4. If below zero *F and/or you'll be out for days, use a Vapor Barrier Liner (VBL) as your first blanket layer to mitigate evaporative heat loss. This can be any plastic sheet, rain poncho, emergency foil blanket, etc. VBLs not only reduce heat loss but also keep your gear lighter. (Frozen water vapor is heavy.) The color (even reflective silver) doesn't matter one bit because radiative heat lost is (delta T)^4 and the delta-T is near zero.
5. Wear a thin poly (wicking) balaclava and thick loose fleece balaclava at bare minimum. I sometimes wear a stocking cap in between.
6. Wear your wicking - fleece - puffy layers of winter clothes to bed. (Except if you've a VBL, then puffy layer goes outside of VBL.) Your shell / parka can go atop or underneath. Insure yer not cramped or constricted in the least; all layers and stuff should feel loose.
7. Bring your boot liners, hot water-bottle**, chemical heat packs (as a late night back-up), and mitten liners to bed. ** Only use a highly-trusted, never-will-leak bottle. Fill with near boiling water, put inside insulated bottle holder, and use to keep feet warm.
8. Use a snowshelter, tent, tree-cover and/or anything else to block the wind, add some warmth, and radiative heat loss to the sky.
9. Go to bed warm -- eat well, jog a lap around camp.
10. If cold at night, do sit-ups.