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Thread: Baffle height

  1. #11
    cmc4free's Avatar
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    Quote Originally Posted by stevebo View Post
    Hey guys, Im working on a 0 degree under quilt for a bridge hammock- how thick should the baffle be for 0 degree? What about 20 degrees? Thanks!
    Not picking on Steve here at all, because I inadvertently made the same mistake in my wording, but for the sake of accuracy in terminology...

    A down quilt is divided into chambers. The maximum height of the chamber, which vendors list in their specifications as loft height, is shown on this graphic as Hc. The chambers are separated by strips of mesh sewn between the inner and outer shells, which are called baffles. The height of the baffles are shown on this graphic as Hb.



    What gets a little dicey with a differential cut underquilt, is that as it's suspended from the hammock and curves to fit the occupant, the differential cut allows the outer shell to expand more than the inner shell, such that Hc and Hb become closer to being equal. However, I still believe most vendors are probably specifying loft height (Hc) with the quilt laying flat on a table. That's how it's always shown in photographs when there is a ruler held up against the quilt.





    Graphics extracted from the CatSplat Differential Underquilt Calculator.

  2. #12
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    I hear what you are saying but since he asked about baffle height, how does that affect the rating (or at least the actual cold/warmth of the quilt)? If you imagine a 6" tall chamber but a 3" tall baffle, wouldn't that lead to colder spots at the baffles? Sewn through quilts being the extreme case.

  3. #13
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    Quote Originally Posted by scrope View Post
    I hear what you are saying but since he asked about baffle height, how does that affect the rating (or at least the actual cold/warmth of the quilt)? If you imagine a 6" tall chamber but a 3" tall baffle, wouldn't that lead to colder spots at the baffles? Sewn through quilts being the extreme case.
    tl;dr below, I know...

    Part of the reason for my previous post was wondering if he actually meant chamber height, when he said baffle height, for example in the title of this thread. Sometimes the term "baffle" is used to refer to the entire chamber (whether it's sewn through or not), and sometimes it is used to refer to just the vertical pieces of mesh or other fabric that connects the inner and outer shells and creates the divisions between each chamber. Quilts, sleeping bags, comforters, jackets, etc. that have that construction are also sometimes referred to as having box-baffle construction. That term at least makes it pretty clear the style of construction that is used, but the terminology can still be a bit nebulous from person to person as to whether "baffle" means the entire chamber or just the vertical strips that separate the chambers.

    For the example you gave, I'll first reply with my thoughts based on a laboratory type test setup. If a differential cut quilt with chambers that were 6" tall at their maximum points but only 3" tall at the baffles, was laid flat over a flat heat source, there would be more heat loss at the 3" minimum height areas than at the 6" tall maximum areas. No question. If you viewed such a test through an infrared camera, you'd see that plain as day.

    Not all quilts (especially topquilts) are differential cut though, and in those cases there may not be as pronounced a difference between Hc and Hb (it probably depends on how much down each chamber is filled with, or basically how "puffy" each chamber is). The whole purpose for a differential cut is that so when we move outside that unrealistic laboratory example and start hanging this underquilt under a hammock, or draping this topquilt over a body, the loft of the quilt isn't compromised by the curvature of the shells. When the differential quilt is curved as it's intended to be, again there may not be as much of a difference between Hc and Hb. But in the end, there will always be more heat loss through any area that has less distance between the heat source and the colder ambient temperature (at least assuming a homogenous distribution of insulation inside the shells and not empty pockets of air where there can be additional heat lost through convection currents within the quilt).

    The sewn through construction is rarely used in quilts that are designed to have good performance in colder weather. You see that type of construction on lower cost comforters that are made for use in the home, for some lightweight outdoor quilts that are rated 50-60 or thereabouts, or in lower-performance, lower-cost outdoor gear that isn't rated at all. In these cases, I'm sure there is more heat loss through the seams than there is in the lofted areas, but it's not as much a concern because they wouldn't be used when the ambient temperature is very cold, so the occupant is probably unlikely to notice those distinct warmer and colder areas. The more loft the quilt has, the greater differential there would be between heat loss through the seams and heat loss through the lofted areas, though again, it's not common to find this sort of construction on down quilts that have more than an inch to inch and a half of loft.

    A counter-example is in down apparel. Sewn through construction is a lot more common in that case, though there are box-baffled down parkas and such, as well. I don't own any clothing with actual box-baffles, but I know of at least a few examples like the Patagonia Grade VII down parka I coveted at one point in time. I'm sure there are numerous examples, and I bet they all cost a pretty penny.

    One other sewn through example (often used in apparel for that matter) is in the case of certain synthetic batt insulations that require quilting. I believe Primaloft Gold, for example, requires quilting whereas Climashield Apex does not. Again, I'd assume in those cases, the heat loss would be greater in the seamed areas than the quilted areas.

    Wearing a wind or rain shell over the top of a sewn-through jacket would reduce the heat loss, but now I'm really starting to drift off topic.
    Last edited by cmc4free; 02-06-2020 at 15:06.

  4. #14
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    Thank you cmc4free for your indepth response. I kind of thought that 'loft' was the amount of poofiness each chamber had at full expansion. I think using loft rating for temp rating is slightly misleading as the baffle height is the thinest point in the UQ and therefore the coldest- the baffle height should be the height used in determining the quilt rating-making it a more universal guideline.

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    The baffle area is a small percentage of the total. The average loft is a good measurement to use for ratings. That's what your body feels.

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    Disclaimer that I'm not 100% certain about everything I've said. In some cases, I'm making reasonably educated assumptions. I'm not a quilt manufacturer, nor a spokesperson for one, so only they could tell us for sure what they are specifying.

    That said, I don't feel mislead in any way, personally. What matters to me in a quilt is that it performs to its rated temperature. I own down quilts from Warbonnet, UGQ, Hammock Gear, Loco Libre, Enlightened Equipment, and Jacks R Better, and none of those have ever let me down in terms of performance to their temp rating.

    Now, since the subject of this thread is DIY and how much loft to use, one could err on the side of caution and make the baffle height according to the desired loft, such that the maximum chamber height is even thicker. In that case though, one would have to be careful to fill each chamber with enough down to fully loft it, otherwise the quilt won't be able to perform to its potential.

    Using the CatSplat calculator, you can enter the desired Baffle Height, Maximum Chamber Height and other variables and the spreadsheet will calculate the fabric widths to create the differential shape, how much down to fill each chamber with, and also estimate the temperature rating. In fact, the calculator estimates the temperature rating based on "Average Loft" which is the average of Hb and Hc. The calculator was used to check the temperature ratings of a few different Hammock Gear and UGQ quilts and the results were within 3 of the manufacturer's ratings.

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    Thanks cmc4free for your detailed response. I've been wondering about this issue since I did a DIY quilt and accidentally overstuffed it way more than I intended. This is because I was using reclaimed down and just grabbing it by the handfuls and guesstimating how much to put in each chamber. The result was *way* puffier than I intended and the box was much higher than the baffle length. I was sure it was going to be at least as warm as the baffle height suggested but it got me thinking about it.

    The side effect to my DIY was some slight weight penalty but the main issue was a shortening of the width of the quilt since more of the fabric went vertical, i.e., my square boxes became tall rectangles. What I gained in puffiness I lost in width coverage.

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    Senior Member BillyBob58's Avatar
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    Steve, my JRB dual differentially cut GL4 UQ, rated at 0F, specs a 3" baffle along with a loft rating of 3.5". Keep in mind that a number of people have reported being warm at zero or below. I can only vouch for toasty at 10F, under a JRB bridge hammock, the coldest I have tried to use it. But also keep in mind that "dual dif cut" business, which I assume works to increase the warmth rating of an UQ. So, I don't know if, without such an approach, a slightly higher baffle and loft height might be needed.

    For my 20F MW3, the baffles are 2" and loft rated at 2.5".It has kept me toasty, with no other layers than cotton PJs, at 25F also under a JRB bridge hammock.

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    Sorry guys, I didn't mean to start an argument or controversy ! What I meant was what dimensions do I need to make the no see um netting baffle for a set temp rating-------(great responses--sooo much good information!) I see now, that baffle height is just a small part of the equation---chamber width etc .
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    Quote Originally Posted by stevebo View Post
    Sorry guys, I didn't mean to start an argument or controversy ! What I meant was what dimensions do I need to make the no see um netting baffle for a set temp rating-------(great responses--sooo much good information!) I see now, that baffle height is just a small part of the equation---chamber width etc .
    Heh stevebo- no worries here as I was looking for a starting point for baffle material used height in determining the quilts rating. Basically your question and I think the answer is-we are working with variable trapazoids so any dimension change effects the volume/loft. ie; if you had a chamber with a large distance between the baffles the volume of the chamber could be the same as one that had less distance between baffles but had taller baffles. Well- the loft is going to vary because the quilt material poofieness/loft allowed between the baffles will become less as the distance between each baffle gets closer to each other.
    Excuse the roundabout on my part-I'm just trying to understand the design principles before commiting to my first down UQ.

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