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Insulation Measurement
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Aaron Sorensen
(awsorensen) - MLife

Locale: South of Forester Pass
Re: Re: Insulation Measurement on 06/18/2012 12:11:00 MDT Print View

Jerry,

I agree, but to have a test measure these results would be great.
I could see a light summer weight inflatable air mattress with a bag with more loft and a total weight much less be proven to work better than what people normally use during the winter.

Then again, I would like to be proven wrong and be able to find what that perfect set up would be.

Edited by awsorensen on 06/18/2012 12:11:57 MDT.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
"overfill" v.s. "underfill" on 06/19/2012 23:48:05 MDT Print View

The best example I can give of "underfill" is Mountain Hardware's "Phantom 32" sleeping bag. (Good name for a bag with a "phantom temp rating".)Had a MH Phantom 32 but never used it and returned it to REI once I saw the great loft in a Western Mountaineering Megalite 30 F. bag.

But even the Megalite lacked enough warmth on a 24 f. night in the Sierra Nevadas so I had WM overfill it with another ounce of down (850 cu. in. more down). That, I think, will solve the problem and make it a 20 F. bag, which is usually recommended for Sierra and Rockies summer nights above 8,000 ft. The bag sure LOOKS like it's overfilled.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: "overfill" v.s. "underfill" on 06/20/2012 08:08:32 MDT Print View

When you say the Phantom was "underfilled" - were there places where the shell and liner fabric were touching each other with no down between them?

Dave U
(FamilyGuy) - F

Locale: Rockies
Re: "overfill" v.s. "underfill" on 06/20/2012 08:51:33 MDT Print View

Years ago I had a Phantom 32 and thought the loft was excellent (you can see that they are EN tested and true to rating). The WM had 'maybe' a little more loft but it was also noticeably slimmer. Less fabric and similar down fill means the loft will appear higher.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: "overfill" v.s. "underfill" on 06/20/2012 10:12:51 MDT Print View

Having NO down between layers of fabric is a pretty clear case of underfill. But even this term is difficult to define with any accuracy. Very dry down will perform differently than damp down will perform diferently than wetter down, will perform differently than soaked down. I suggest that filling the bag might not be accurate between days to say. Some manufaturors are known to consistanly underfill bags and quilts slightly. Others to consistantly overfill slightly.

The correlation between loft and insulating value is fairly well established, refering to the EN system. Measurements for both fill type and and bags have been firly well done. Highly ignored was wind resistance of various fabrics, wet performance (though this was done partially here by Ryan et al), and a host of other factors, such as compression of down when multiple layers are used (or even when in thick artic bags, ie, -20F and below, touched on in the article.) Even a super light bivy will compress a bag somewhat, but this compression is often offset by the reduced air convenction...soo, we consider a bivy to be a bit warmer (even though it reduces loft by as much as half an inch.)

In less than perfect conditions, a bit of overfill is always needed to maintain some loft. It is like paint on a car. They use enough to cover it, then use more to cover against minor scratches. Bag manufacturers don't like that methode though. It means more (expensive) down stuffing. And, weight is always a factor. 2oz in an otherwise 16oz bag will often mean the difference between a purchase and looking elsewhere. As Ultralighters, this is one of the trade offs we make for weight controll vs being warm enough. Or, adding another layer of baffeling to stop internal convection. . .again expensive.

I think this was a good atricle, and, stands firm as a jumping off point for others examining some of the finer details of synthetics vs down and combination bags.

Well done, as I said before. Thanks Jerry!

Andrew Bishop
(copperhead) - M

Locale: Down Under
Quilting synthetics on 06/20/2012 13:27:57 MDT Print View

" The problem with insulation is flow of air inside. For example, an un-insulated air mattress has a lot of internal airflow, so it doesn’t provide very much insulation."

Jerry - I infer from this that sewing a criss-cross pattern into my synthetic quilt will improve warmth by reducing internal air flow. Is that correct?

Andrew

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Quilting synthetics on 06/20/2012 14:16:19 MDT Print View

No - quilting would create thin places so it would be worse

I speculate that in my test, since the insulation was horizontal, the air flow was vertical. You could have some insulation, then a layer of something that impeded air flow, then another layer of insulation, but the layer of something would weigh more than anything gained.

When I put a layer of eVent on top it improved the insulation. I speculate that that impedes air flow inside the insulation. So, by choosing the right material for the top you could improve your insulation. I think eVent weighs too much so you'de be better off with lighter weight fabric and a little more insulation.

But then what about if it's windy?

I think I have rasied more questions than answers : )