Zipper Modification
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 David Lewis-Gever (dgever) - F - MLife Locale: Brooklyn Zipper Modification on 03/08/2010 07:58:07 MST I have a Marmot Helium with a 1/2 zipper that I would like to convert to a full zipper. I definitely don't have the skills to do this, so does anyone know where I can get this done? I am also thinking of having some additional down inserted since the bag would already be cut open.I would imagine that converting it into a quilt would be easier, but at the intended temp I think the draft would be troublesome.
 Travis Leanna (T.L.) - MLife Locale: Wisconsin Re: adding down on 03/11/2010 12:23:54 MST I may have completely misunderstood, but I just read a thread where Richard Nisley said that the optimum performance of down was at a 2.5x compression. I don't have the actual thread, but here's a quote from another thread, basically dealing with the same thing. However, these are mathematical equations that aren't true in all circumstances for all people."So, assuming I have understood this right, in the linear region of the curve (where UL backpackers operate) if you decrease the thickness of your typical UL sleeping bag by a factor of 2, you will not affect the warmth of the bag. Why? Because the density will be doubled, and so the clo/inch will double, but the thickness will be halved... so 2*0.5=1 and the warmth of the bag will stay the same.I think is a particularly interesting fact. Surely it means that you needn't worry so much about needing lots of room inside your sleeping bag or hard shell to allow a down jacket to loft fully. A partially compressed jacket should be just as warm, so long as you are not completely crushing it (eg. lying on it!)."
 Nicholas Miller (nmiller08) - F Locale: Montana down compression on 03/11/2010 12:40:21 MST This is my understanding too, based on several threads/posts from Mr. Nisley and others. There was even a comment a while back regarding why "fully lofted" has become the marketing standard due to the numbers game manufacturers have to play with each other. ("yeah, well we get 7" of loft!!). Anyway, I took this "optimum density" thing and ran with it recently on a down sweater for my girlfriend. Each compartment was stuffed to approximately 2x density. It has proven, at least anecdotally, to be quite warm for it's thickness. Edited by nmiller08 on 03/12/2010 15:29:53 MST.
 Richard Nisley (richard295) - M Locale: San Francisco Bay Area Re: Re: adding down on 03/11/2010 16:39:16 MST The insulation value is about the same in the range from fully lofted to 2.5x density increase. Down isn't warmer at 2.5x density.
 Travis Leanna (T.L.) - MLife Locale: Wisconsin Re: Re: Re: adding down on 03/11/2010 16:44:12 MST In the case above though, adding down--to an extent--would increase warmth since there is more of it, and the slight compression of adding more down would not be a detractor of the insulating properties.Or did I just botch the whole concept?
 Nicholas Miller (nmiller08) - F Locale: Montana Re: adding down on 03/11/2010 18:16:23 MST Sounds right to me Travis, it seems the difference is the two possible scenarios...here we're talking about filling a fixed space with more and more down (warmer and warmer, but diminishing returns beyond 2.5x even though warmth continues to increase) and the alternate idea of shrinking a space with a fixed amount of down in it (retains it's warmth up to 2.5 compression, then actually loses insulation value).
 Kevin Beeden (captain_paranoia) - F Locale: UK Re: adding down on 03/12/2010 07:52:09 MST > In the case above though, adding down--to an extent--would increase warmth since there is more of itI'm not sure that's what Richard has said (and I'd appreciate a more detailed explanation from Richard, or a pointer to his investigations).My understanding is that it's not the down that insulates, it's the air trapped within the down that insulates (the 'dead air space'). All the down does is expand into the space provided between the shell layers, and prevent air circulating (thus preventing convection losses).Since down is made from a solid, it must conduct heat better than air, so, if you replace the air with down, the insulation will be reduced. On the other hand, I can see that increasing the down filling slightly may further reduce convection within the down cells, and thus improve performance.At the limit case, where we ram in so much down that the bag is a solid mass, we no longer have dead air; we have a fairly conductive, solid lump of keratin.I note that Richard said:"The insulation value is about the same in the range from fully lofted to 2.5x density increase. Down isn't warmer at 2.5x density"If I understand the second sentence properly, Richard is saying that increasing the amount of down over the fill density will not make the bag warmer, which would tally with my thinking. Edited by captain_paranoia on 03/12/2010 07:54:54 MST.
 Travis Leanna (T.L.) - MLife Locale: Wisconsin Re: Re: adding down on 03/12/2010 08:07:54 MST I found the thread dealing with this. http://www.backpackinglight.com/cgibin/backpackinglight/forums/thread_display.html?forum_thread_id=12505&startat=20Here's a graph from Richard that I think is relavant.Quote Richard: "You can make a down bag or clothing warmer by increasing its density even if the loft is less." Edited by T.L. on 03/12/2010 08:10:33 MST.
 Richard Nisley (richard295) - M Locale: San Francisco Bay Area Re: Re: adding down on 03/12/2010 09:12:22 MST Travis and Others,Thank you for attempting to help Kevin understand by pointing him to some of the prior relevant discussions on this topic.Kevin,Heat will transfer through three mechanisms simultaneously (conduction, convection, and radiation). The convection is effectively stopped when the volume of the baffles matches the fill power of the down. By continuing to overstuff down beyond its fully lofted amount, the air pocket sizes will continue to be progressively reduced (results in less conduction heat transfer) and the increasing filament intersections with the radiation (results in less radiation heat transfer).
 Travis Leanna (T.L.) - MLife Locale: Wisconsin Re: Re: Re: adding down on 03/12/2010 09:32:35 MST Thanks for checking up on us amateurs, Richard! Your posts are most informative.
 Diplomatic Mike (MikefaeDundee) Locale: Under a bush in Scotland Re : Down fill on 03/12/2010 09:39:14 MST "The convection is effectively stopped when the volume of the baffles matches the fill power of the down. By continuing to overstuff down beyond its fully lofted amount, the air pocket sizes will continue to be progressively reduced (results in less conduction heat transfer) and the increasing filament intersections with the radiation (results in less radiation heat transfer)."This puzzles me too. As the conduction is reduced as the air pockets get smaller, isn't it simultaneously increased as the pathways across the down become more numerous?
 Richard Nisley (richard295) - M Locale: San Francisco Bay Area Re: Re : Down fill on 03/12/2010 11:02:49 MST Mike,Yes it is but, to a lesser degree that the other heat-transfer-mechanisms positively offset its negative influence. This positive offset region averages approximately from fully lofted density to 2.5x fully lofted density. Edited by richard295 on 03/12/2010 11:06:16 MST.