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.