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  1. #1
    Registered User Big Dawg's Avatar
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    Default Insulation question

    If I'm making a synthetic underquilt from a +40 rectangle bag,, & I double up part of this quilt (2 layers of +40), does this doubled section keep me warm down to 0 degrees??? Doubt it,, but what would 2 layers of +40 bring me down to? Any ideas?

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    Registered User Patrick's Avatar
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    A general formula I've seen is to take the loft in inches, multiply it by 40, then subtract that product from 100 to get the rating. So, a bag with 1.5 inches of loft will give a bag that is comfortable down to around 40 degrees (1.5 x 40 = 60; 100 - 60 = 40).

    I'm sure this is pretty rough, but my quilt is 1.5 inches or so and feels good at 40, so I feel like it's at least in the right neighborhood.

    Assuming then that your bag has 1.5 inches of insulation, three inches using this formula would yield warmth down to -20 (3 x 40 = 120; 100 - 120 = -20).

    I'm not sure how well the formula holds up when you get down to negatives, but it seems like three inches would get you down mighty low.

    Anyone know if the same rules apply to underquilts as sleeping bags or quilts on top? Heat rising or anything like that affect things?

  3. #3

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    thermodynamics. heat moves from hot to cold. So, you gotta stop it. More loft is more barrier. so, either on the top or the bottom, the heat wants to go to the cold- wants to heat up the stuff around it (because cold doesn't exist, it's just the lack of heat, just as dark is the lack of light) It's the same reason a light-bulb lights up a room- the light goes everywhere.

    So, the heat spreads out. If you warm up the area around you, you are warm. The problem with the hammock is that: "ok, we've heated up the area around the hammock- darn, the air moved. ok, we've heated up the area (air) around the hammock, darn..." The insulation stops that- (it "insulates" or stops the heat from going so fast.) It's also the principle behind the wetsuit- ("ok, we've heated up the water around the diver- darn...")

    titanium
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    Patrick,

    I have seen that equation also but I don't believe it. What it is saying is that at 100°F you don't need any insulation but starting at that point you get 40°F worth of insulating value for every 1 inch loft of breathable insulation... that means you need 1/2 inch of insulation at 80°F. That is just fundamentally flawed... just as what you computed is (3 inches of insulation for -20°F). My best guess is that top side insulation is best defined by:

    [temperature rating °F] = 70 - ([thickness inches] X 20)

    This agrees with 40°F for 1.5 inches of loft but yields 10°F for 3 inches of loft. If you go look at Western Mountaineering specs I think you will find this somewhat consistant with their bag's ratings for their narrow cut mummy bags.

    But this is for top side insulation that gravity gently drapes on top of you. On the bottom side of a hammock gravity doesn't work for you and it is a bit of a struggle to get the fit right so that you aren't overly compressing the insulation while at the same time introducing unwanted ventilation... so you are not likely to get 20°F per inch of insulation.

    Youngblood

  5. #5
    Section Hiker, 1,040 + miles, donating member peter_pan's Avatar
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    I agree with Youngblood on the formula point and that 3 inches is more like 10 degrees...further correlation is that a 6 inch loft sleeping bag means 3 on top and 3 on the bottom and many bags with this stated loft are rated between 5 and 20 based on how conservative the manufacturer...

    As far as the gravity issue I disagree, especially on high quality down...What make high quality down viable for very light bags and quilts is the considerably lighter shell material nylons currently available...Heavier nylons 1.6, 1.9 oz/ sq yd may actually inhibit the full loft by their very weight... this is frequently compensated by overstuffing to ensure the loft...The tops of bags and quilts have gravity working against the loft...yes, Youngblood is right in that gravity lays the bag on the sleeper without an air space... but the other point is... that gravity works against the upward loft of down...this is exacerbated by excessive tucking of a bag on the side and shifting of positions... when material is drawn tight it serves to further tension the top side of the outer layer, further inhibiting the full loft....As a point of example, think how many times as a ground sleeper when cold knees, feet, elbows or shoulder awoke you...these point poke at the shell, material is drawn tight, loft is reduced and you feel cold on that spot...normal solution , shift and refluff that area.

    The statement on gravity working against you on a properly hung under quilt is flat wrong...in fact, it is exactly the opposite, gravity works for the Under Quilt and Pea Pod. Both of these items when hung properly in accordance with their respective instructions place the inside of the shell gently touching the hammock bottom....gravity pulls the down, baffling and outer shell surface down to its full extension of loft...It is virtually impossible to experience tension cold spot on the underside of a hammock using a properly suspended Under Quilt or Pea Pod. There are many reports of users of down under quilts with 1.5 inches of loft experiencing warm comfort at 25-30 degrees and uninterrupted nights of sleep. .. These are results beyond traditional expectations of 1.5 inches of loft…I submit it is because of the effectiveness enhancement of the effects of gravity on Under Quilts.

    Moreover, consider this. Many report feeling the heat radiating back almost immediately when in a hammock with a down Under Quilt or Pea Pod…realize that heat primarily rises…we regulate body temperatures regularly by putting on or removing hats etc….heat rises into the bag top or top quilt…the amount of loft holds and slows its eventual loss and if tensioned even allows the intrusion of ambient cold….By contrast, Under Quilts and Pea Pods, receive heat initially that wants to naturally return upward to the sleeper as much as it want to proceed outward, …as the loft is filled with heat this natural propensity to rise returns even more heat to the sleeper… Plus, as stated above, because of gravity it is very unlikely that the ambient cold will find a tension point( thin spot) to invade this warming zone.

    But then I’m Biased.

    Pan
    ounces to grams
    WWW.JACKSRBETTER.COM home of the Nest and No Sniveler underquilts and Bear Mtn Bridge Hammock

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    Registered User briarpatch's Avatar
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    Another issue you may have in trying to double up the thickness is the width of the sleeping bag you are using. I've found that you can't skimp on width for an underquilt (or length either, for that matter). If the rectangular bag is a 36 inches wide, it probably won't be wide enough to eliminate cold spots.
    A bad day on the trail beats a good day most anywhere else.

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    Registered User Patrick's Avatar
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    That formula looks much better; thanks for posting that. I'm looking forward to testing some of this stuff out this fall and winter.

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    Registered User Big Dawg's Avatar
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    Patrick, my original idea was to use a mummy bag (b/c of better insulation for the weight), & could have used a mummy style bag for the design posted on your thread ("I made a synthetic underquilt"), but because of info from this thread, I think I'll just use the bag that you used, NF Allegheny-(rectangle bag, (L) = 83" x 65" opened up like a quilt). I would cut that down to 83" x 48",, & voilla, a rectangle synthetic underquilt,which would give me ample coverage like the JRB Nest. My only original concern w/ that was the +40 rating. I mostly hike fall/winter/spring, which I knew would need lower than +40, which is why I was considering taking that extra piece left over from cutting down the bag (83" x 17") & sewing it diagonally onto the 83" x 48" piece (in the same diagonal position that I would be laying most of the time), giving me a rating closer to +10 along the diagonal. This would mean that my underquilt would be close to 2 lbs 9 ozs,, ouch. For this reason, I may leave that extra 83" x 17" piece off. Like Peter Pan said, for underquilt insulation, I may be able to get down to +25 to +30 w/ a +40 underquilt. The hammock idea is still in the wish list category,,, I'm just covering all the bases before I commit. I'm currently trying to reduce my base weight, which now is about 35 lbs. Based on my current wish list, I can get my base weight down to 16+ lbs w/ a tarptent, or around 19+ lbs w/ a HH & insulation for fall/winter/spring camping. From all I've heard, that extra few lbs is worth it!!
    Last edited by Big Dawg; 09-16-2005 at 07:45.

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    Registered User Jaybird's Avatar
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    Default make???

    Quote Originally Posted by Big Dog
    If I'm making a synthetic underquilt from a +40 rectangle bag,, & I double up part of this quilt (2 layers of +40), does this doubled section keep me warm down to 0 degrees??? Doubt it,, but what would 2 layers of +40 bring me down to? Any ideas?

    WHY RE-INVENT the wheel???

    OR in your case a sleeping bag...large manufacturers do it better...do it cheeper (because of quantity manufactured)...& probably have better quality (no slam intended..but, you are "experimenting").

    Put the needle & thread down...buy you a MUMMY BAG & be done with it!
    see ya'll UP the trail!

    "Jaybird"

    GA-ME...
    "on-the-20-year-plan"

    www.trailjournals.com/Jaybird2013

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    Default Gravity As I Understand It

    Quote Originally Posted by peter_pan
    ...The statement on gravity working against you on a properly hung under quilt is flat wrong...in fact, it is exactly the opposite, gravity works for the Under Quilt and Pea Pod. ...
    For what it is worth, this was statement, not what you seemed to say it was:
    Quote Originally Posted by Youngblood
    ...But this is for top side insulation that gravity gently drapes on top of you. On the bottom side of a hammock gravity doesn't work for you and it is a bit of a struggle to get the fit right so that you aren't overly compressing the insulation while at the same time introducing unwanted ventilation... so you are not likely to get 20°F per inch of insulation.
    I don't have one of your Under Quilts, but I would bet money that gravity doesn't hold it snuggly to the bottom of a hammock. In fact, gravity wants to pull it to the ground. It is your suspension systems that holds it to the bottom of the hammock. Your suspension system has to oppose gravity and it has to hold just right. If it is too tight you compress too much down and lose insulation that way and if it is too loose you get too much ventilation and lose effective insulation that way. Now, if you use your Under Quilt as a top side quilt, gravity does work for you and it gently drapes it over your body without a suspension system. This is the way gravity works as I understand it... but if my understanding of gravity is in error, I extend my apologizes.

    Youngblood

  11. #11
    Registered User Patrick's Avatar
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    Quote Originally Posted by Big Dog
    I'm currently trying to reduce my base weight, which now is about 35 lbs. Based on my current wish list, I can get my base weight down to 16+ lbs w/ a tarptent, or around 19+ lbs w/ a HH & insulation for fall/winter/spring camping.
    I'm sure true winter camping is going to add some decent weight, but comparing apples to apples, my three-season set-up with a hammock actually saved me weight over my previous three-season tarp set-up.

    Old stuff:
    Ground sheet (2 mil plastic, about 8' x 4') - 10 oz.
    Sleeping pad (8 section Z-Rest) - 9 oz.
    Sleeping bag (20 degree Cat's Meow) - 48 oz.
    Bug netting - 5 oz.
    Silnylon tarp (modified 8' x 10', including bag, stakes, and all lines) - 20 oz.

    Total: 92 oz (5.75 lbs).

    New stuff:
    HH ULB (including stakes, lines, bag, straps, and fly) - 32 oz.
    Homemade Ray-Way quilt - 28 oz.
    Homemade modified sleeping bag underquilt - 24 oz.

    Total: 84 oz (5.25 lbs).

    Both set-ups could be lighter, I'm sure. I don't do down, though, which is where I think most of the weight savings would come from. Either way, there's no way that, for comparable set-ups, you're going to be adding pounds with a hammock set-up. As you can see, there's a good chance that you'll actually lose weight.

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    Registered User Patrick's Avatar
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    Also, I think variable thickness is a very interesting idea. I've read of others doing so with a sleeping pad for the critical areas and I think what you're saying has a lot of potential. I've been sort of planning to make an underquilt from scratch that would be a bit thicker than my current one (I think I could do it for the same weight or less). I'd then be able to use one or the other or both to get a pretty wide range of comfortable temps covered.

    It's an interesting idea to maybe make a narrow one. You could use it alone in the summer or as additional insulation in the fall or winter. Or maybe if the temps were going to change a lot, you could bring it and only really focus on staying strictly on it when it was a particularly cold night.

    It's official. You're the guinea pig. Get this thing sewn up and report back.

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    Quote Originally Posted by Patrick
    Either way, there's no way that, for comparable set-ups, you're going to be adding pounds with a hammock set-up.
    I also cut weight going from my ground setup to a hammock setup, but it doesn't work that way for someone who's already a lightweight ground sleeper. You can get much lighter with a ground setup, but hammocks are so much more comfortable.

    These numbers are for roughly 35F and aren't even using the 5 oz tarps at BPL...

    13 oz - JRB 8x8 Tarp w/ 4 stakes and cord (use hiking poles or trees)
    7 oz - CCF pad (not full length...use backpack under knees)
    16 oz - 32F down bag
    5 oz - Bugnet
    - Total - 35 oz

    11 - Homemade Speer (w/o bugnet)
    03.5 - Speer SPE (use clothes for wings)
    10 - Equinox CCF Pad 20"x72"x3/8"
    16 - Speer Top Blanket
    11 - JRB 8x8 w/ 2 stakes and cord
    - Total - 51.5 oz

    Using Jack's setup from JRB...possibly good to 25F:

    16 - HH Extreme light Racer w/ tree savers
    11 - JRB 8x8 w/ cord and 2 pti pegs
    42 - JRB Nest, No Sniveller, suspension
    - Total - 69 oz

  14. #14
    Registered User Big Dawg's Avatar
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    Quote Originally Posted by Jaybird
    WHY RE-INVENT the wheel???

    OR in your case a sleeping bag...large manufacturers do it better...do it cheeper (because of quantity manufactured)...& probably have better quality (no slam intended..but, you are "experimenting").

    Put the needle & thread down...buy you a MUMMY BAG & be done with it!
    Huh? There is no one who offers a synthetic "nest" underquilt for a hammock. That's why I have to make one. A mummy bag wouldn't work as good, because of the smaller dimensions at the foot end,,,,,, tell me what I'm missing,, cause I'm all new to this stuff

    By the way, I'll be using my NF mummy bag inside the hammock as a top quilt.

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    Quote Originally Posted by Jaybird

    Put the needle & thread down...buy you a MUMMY BAG & be done with it!
    Where's the FUN in that?!

  16. #16
    Registered User Big Dawg's Avatar
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    Quote Originally Posted by Patrick

    It's official. You're the guinea pig. Get this thing sewn up and report back.
    OK,, you can send me a check to......... hahahaha. Funds are tight, my wife & I are in the process of adopting a baby,,,, so it may be the 1st of next year before I can start acting on my wish list,,,,, but I'll respond once I know,,,, unless anyone out there wants to give to the Big Dog hiking wish list fund! haha

  17. #17

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    making your own gear is so satisfying- especially when someone says: "where did you get that?" "made it" "you did WHAT!?"

    I like making gear! it's fun!

    titanium
    just call me TH
    woman with altitude

  18. #18
    Registered User Big Dawg's Avatar
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    Here's my numbers (from the wish list----actually some items I already have)

    & by the way, I'm a big guy, 6'5",,,, which affects some items bought, making them heavier.

    29 oz - Tarptent Virga w/ sewn-in net/floor (no groundcloth)
    38 oz - +35 NF Flight bag, long (already have)
    24 oz - Thermarest Prolite 3, regular
    Total = 5 lbs, 11 oz


    29 oz - HH Explorer UL, w/o tarp, w/ snakeskins, (stock fly too small)
    19 oz - MacCat deluxe tarp w/ guylines/stakes
    38 oz - +35 NF Flight bag, long, for top quilt (already have)
    32 oz - +40 NF Allegheny bag modified as underquilt (1 layer)
    Total = 7 lbs, 6 oz
    also, w/ HH, I would need to bring a bear bagging kit-I sleep w/ my food in a tent-sealed by ursack odor barrier), & a groundcloth if I had to go to ground.
    Last edited by Big Dawg; 09-16-2005 at 14:07.

  19. #19
    Registered User Seeker's Avatar
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    that's NUTHIN'... MY god is 6'-10" talll and weighs...

    oh wait... i thought this was the 'messege from god thread'... sorry...

    on a serious note, you make a good point... friend of my brother's hiked with us this summer. i had talked with him about gear before we went, and he asked me to go over his gear some time... told me what he had and what it weighed, and i thought it seemed a little heavy for what he was describing... then i realize just how BIG he was... EVERYTHING is a size XXL... sleeping bag is the long model. pack is the largest version of a popular one (due to his torso length). rain gear was a couple ounces per piece heavier... big shoes weigh more than some others... needs a larger tent... jacket was heavier. even a t-shirt weighs a little more... you get the idea... i was surprised. just something i'd never considered before....

  20. #20
    Registered User Big Dawg's Avatar
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    Quote Originally Posted by Seeker
    that's NUTHIN'... MY god is 6'-10" talll and weighs...

    oh wait... i thought this was the 'messege from god thread'... sorry...

    on a serious note, you make a good point... friend of my brother's hiked with us this summer. i had talked with him about gear before we went, and he asked me to go over his gear some time... told me what he had and what it weighed, and i thought it seemed a little heavy for what he was describing... then i realize just how BIG he was... EVERYTHING is a size XXL... sleeping bag is the long model. pack is the largest version of a popular one (due to his torso length). rain gear was a couple ounces per piece heavier... big shoes weigh more than some others... needs a larger tent... jacket was heavier. even a t-shirt weighs a little more... you get the idea... i was surprised. just something i'd never considered before....
    LOL,,, you're funny!!

    6'10",,, good gosh,,, I thought I was tall.

    It does make a difference..... but I can handle it,,, cause I'm a big burly Big Dog

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