"Work to Live...Don't Live to Work!"
FF, Et al,
If you are asking the rating estimate for top bag use in a hammock.... A normal full bag used as a quilt, with adequate insulation below you, will do better than its rating.......
Consider this... center of the shoulder to center of the shoulder you are 30-32 inches wide.... Your bottom wrap takes care of bottom and sides well passed center shoulder.... A regular bag opened is 62-66 inches wide.... you only need 4-5 inches to tuck in on each side.... therefore you have 52-56 inches of bag to cover 30-32 inches of you..... So you lay it loosely as to almost accordian the excess and you now have 150-200 % ore lofted bag abve you....better performance.
Note to all.... When cold folk start pulling the bag / quilt closed to eliminate any air space.... so far, so good.....HOWEVER, most end up snugging the bag/quilt too far, effectively reducing loft...not good...Think about it, there is a design requirement for a certain degree of looseness to allow the insulation to reach full loft, for max effectiveness.... the ground dwellers further exaccerbate the problem by moving around, changing positions and poking a knee, elbow, shoulder, foot etc into the tightly drawn material creating a thin spot .... then there is rapid cold invasion....( not unlike the hammock bottom/side issues.
There really are a lot of ways to incorrectly use a sleeping bag/quilt... Another is to continue using a 3/4 light weight summer pad and expect to be warm because you swithed to a 10-20 degree bag...cold feet and legs will defeat this plan....
Warm is as much a thinking game as anything.... When not comfortable the first thoughts should be where is the cold coming from, why, what can one do to eliminate the problem... then what can you do to add more capability/insulation.... for example if your feet are cold... and you already have on a warm pair if socks ... and you are using the summer pad as in the above example you will be better off putting extra socks or shirt/jacket under your feet than on them ( which BTW is often is a double wammyfor reduction of circulation, as well).
So in the end.... The real issue is what is the loft between the ears.
Ounces to Grams.
www.jacksrbetter.com ... Largest supplier of camping quilts and under quilts...Home of the Original Nest Under Quilt, and Bear Mountain Bridge Hammock. 800 595 0413
Nice post Pan. I feel confident about bottom insulation but often wonder how much I need on top.
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does anyone know how companies rate sleeping bags?
are there standards for measurement or ratings, do they have machines or do they just put joe inside the bag and stick him in a freezer till he shivers?
seems like there's mixed standards, like I was reading about the panda bag/hammock I just ordered, it has 3 ratings, comfort, minimum and extreme plus a 5000mm water column rating... which I googled but didn't get much, seems like it's a pressure rating for water proofing, breathability or wind breakage or something... so many factors, i was watching man vs wild and he skinned the fur off some smelly dead deer and then cuddled his water bottle full of warm pee and everything...
so I have 3 questions if anyone knows, one is above
two is how did you come up with this formula?
three is how does water column factor in?
I don't know the answer to your questions but I've seen the 5000mm water thing on tags for columbia and northface jackets and ski pants that claim to be waterproof, windproof, and breathable. Next year's version will probably claim to enlarge your manhood too.
Is this a recommended way to increase warmth? I don't hear much about people doing this, but I have thought about it as an option.
What I know, or think I know:
1) sleeping bag ratings standards - not really any industry standard. Some companies obviously rate conservatively and some do not. Some appear to rate by loft and some by other methods. Best way to use ratings is by checking boards such as this and ones for camping/backpacking to see what others think of a particular manufacturer's rating and then factor in your own factors (warm sleeper, cold sleeper, etc).
2) Some manufacturers will tell you how they rate and why they use the formula they use. Most do not tell you either. I imagine Pan came up with his formula above by a combination of experience and knowledge about insulation. His comments always seem to be pragmatic and founded in logic... which is much appreciated, especially considering he is also a manufacturer.
3) Water column - the number, usually in millimeters, is the height of a column of water that the material will not allow to pass through the material. So, a 5000mm water column rating means the material can keep a column of water that is 5000mm (is that 5 meters?) high from passing through it. These ratings are used to convey waterproofness, as the higher the #, the more waterproof the material is. However, perspiration is not water - it is water vapor and can pass through much smaller spaces than can water. So a highly waterproof material may still be breathable. Used to be, the more waterproof the material, the less breathable. Now things are starting to even out with some technical materials being both waterproof and breathable... and often expensive.
Hope this helps.