Sewn Through Baffle Construction and Its Effect on Warmth

Any loose fill item needs baffles to hold that fill in place and give shape to the item. In most down garments on the market for 3-4 season use the baffles are created by sewing the inner and outer shells together. This separates the fill into separate chambers. However, at some point in time these sewn through baffle lines became fashionable. In my mind, I see it as that classic corporate tension between the engineering department and the marketing department, where the engineering department wants a warm for the weight garment and the marketing department wants to push fashion at a direct expense to performance. It seems that over the years, the marketing departments won out and the market is now dominated by jackets with tiny micro baffles, sometimes as narrow as 1″, all intersecting and skewing off at different angles.

The problem is that every one of those lines is a cold spot, with zero insulation. Furthermore, the narrower the chambers between the lines, the less that fill is able to loft up. So more cold spots and less insulation from the fill. It is true that as the total fill amount goes lower, you need narrower chambers to control it. You need narrower chambers and more lines to control light fill but can get away with wider chambers and fewer lines with heavier fill amounts. However, the industry today is most often putting out jackets with twice as many chambers as you would really need to control the fill amount….at least. Sometimes more.

Over the years I’ve done a bunch of testing on this. Swinging both towards narrower chambers/more control and to wider chambers/less control. Interestingly, even in my most extreme swings toward narrower, I’ve never come close to approaching the density of lines in most mass market jackets. Mostly because it’s soooo excessive, but also because each line has to be sewn. It’s labor intensive. Not only is it detrimental to performance, but it also costs more. I don’t know. These mass market jackets probably just go into a computerized machine that sews like 20 lines at once or something.

I have come to really prefer the widest spacing I can get away with. On multiple occasions, I have built essentially the same jacket back to back. Same calculations. Same fill amounts. Only one with 3″ spacing and the other with 6″ spacing. The difference in R-value is astounding. The level of control is more than adequate in the 6″ spaced jacket. No shifting or open spots at all.

6 thoughts on “Sewn Through Baffle Construction and Its Effect on Warmth”

  1. Why not use a no sewn threw baffle system? The larger chambers arguements are great but it seems you seek the best possible engineering solutions and would at least offer interior baffles eliminating sewn threw seams period. I am very excited to have discovered your company and feel you are craftspeople with pride in your high quality products made in America.

    1. The primary reason is that the calculated loft levels of the SUL and SDUL sweaters are lower than the threshold where there is enough room for a vertical baffle. It must be lower than the loft height by a certain amount to achieve the density needed. The 1.5s start to get near the threshold but the baffle would be so low that it’s worth becomes questionable. When we offer these sweaters in higher calculated lofts, then it might make sense. However, then there is a debate about it. We could box baffle an SUL 2, but we might double the price and add the weight of a baffle system or we could build a sewn through SUL 2.5 for the same warmth (increased fill offsets the baffle efficiency) for the same weight (trading the baffle weight for increased fill) for half the price. At some point baffles clearly make sense. For this in between zone, it is much more nuanced, not just from a cost standpoint, but also from a weight focused perspective.

  2. Given that the Nunatak Skaha UL Down Sweater has a box baffle construction with average 1” loft, Would the SUL 1.5 be comparably warm even though the Skaha uses a fair amount more down (~5oz vs 3.8oz)? They give a static comfort rating of 20F with adequate layering.

    1. It is impossible to use total fill weight as a comparison metric here. The Skaha’s total fill weight is spread over a garment with a hood, insulated pocket, zipper draft tube, different fit dimensions, and whatever else we can’t see. The SUL spreads its total fill weight over none of that and it is all in the body and sleeves. Fit dimensions and taper are likely different too. If you really want a fool-proof comparison you’ll need to ask for the chamber fill calculations. This info is right in the title of the SUL sweaters. 1.5 is the calculated loft. If a chamber is 10″ by 6″, that is multiplied by 1.5 and you find that there is 90 cubic inches of down fill in that space. Divide that by 900 fill power and you find that there is .1 ounces of fill in that space. If you know the quantity of down in any given portion, all those variables above no longer matter. The other metric you’d want to know is measured baffle height. For instance, say the Skaha uses 1.5″ calcualted loft and a .75″ baffle, it is likely a warmer garment than an SUL 1.5 that has 1.5″ calc loft and a 0″ baffle height. If the Skaha uses 1″ of calc loft and a .5″ baffle, then they might end up being pretty similar in overall warmth. The Skaha would have its insulation spread evenly. The SUL would have peaks of high loft, broken up by the sewn through spots with the average landing somewhere similar.

      The take-away is that you need more information to compare warmth. If you were unable to obtain more info, then I would defer to measured loft, rather than total fill weight. Measured loft is not great either, but it is a bit more in the ballpark. An SUL 1.5 will have somewhere between 1.5″ – 2″ measured loft at mid-chamber, split by a sewn through spot every 6″.

  3. Dan, thank you for these thoughtful, detailed, nuanced responses. This level of detail has been sorely missing – especially with respect to down insulation layers. It’s incredibly frustrating to try to compare these in any meaningful way, and it’s clear that the larger manufacturers have zero desire to provide the information needed to do so. The opposite, really: they, even most of the best regarded ones, are far more focused on muddying the waters so you’ll simply buy their product out of frustration. I agree with your notes re marketing vs engineering/performance. You’re at the top of my list for my next orders of down goods.

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