Does down fill power really matter?

[Brett Peugh]

To quote Paul S from a different thread,

‘JCH,

I wondered about that comment too. My understanding of down insulation is that warmth equates to the total volume of dead air space. So, for example, if you have two identical sleeping bags, with the same inches of loft, same size, same construction, then, it does not matter whether it’s 650 fill, 800 fill, 900 file (etc.), all that matters is how many inches of loft there is. And the same should apply for jackets/parkas. So it’s all about the total volume of fill. Folks, if I am wrong, please tell me why. :-) Thanks!’

Box baffles are better than sewn through, but does the down fill power really matter when the same space is being lofted?  Higher fill powers may save some weight but does it really make a difference otherwise?

 

Thank you.

[Jerry Adams]

yes, fill power matters

higher fill power will take less weight of down to fill up the same volume

also, with down, it’s more than just inches of loft.  If you fill a volume just barely, for example you use 1 ounce of 900 FP down to fill 900 cubic inches, it will provide some amount of warmth.

Then, if you add more down, it will add more warmth even though the volume stays the same.  But the efficiency is about half.  For example, if you add an additional 1 ounce of 900 FP down to that 900 cubic inches, it would only add about 50% more warmth as the first ounce.

There are threads about this a few years ago.  Richard Nisely posted some data.

With regular sewn through baffles, the loft is essentially zero where the row of stitches is so it’s less warm.

I’ve used asymmetric sewn through baffles then yeah, the same space is being lofted so it’s the same as box.  I’ve mentioned this before but the idea hasn’t gone viral :)  This is just a 1 foot square test piece but I’ve used it to make quilts and vests:

[Jeffs Eleven]

I think in reverse of that for jackets. (In apparel you can build up more heat/ humidity through work) so I prefer 700fp down so it can handle a little bit more humidity due to having more structure. (Fewer plumes and closer to what would be a feather)

weight and compression aren’t my main concern, it’s humidity control.
maybe theoretical and  too small of a window of efficacy for me to sense, but my momma said I’m special so it’s prolly right.

[Weekend Gear Guide]

Jerry, regarding your comment:

I’ve used asymmetric sewn through baffles then yeah, the same space is being lofted so it’s the same as box.  I’ve mentioned this before but the idea hasn’t gone viral :)  This is just a 1 foot square test piece but I’ve used it to make quilts and vests:

Isn’t this similar to what Rab is doing with their Interstitch Offset Boxwall Baffle Technology, as used in their Rab Infinity Down Jacket (scroll down for diagram and description)

https://rab.equipment/uk/infinity-jacket

[Matthew / BPL]

Whoa, that looks like a really smart way to make sewn through baffles, Jerry.

[JCH]

Love Jerry’s baffles.  Put the “flat side” to the outside and the curve of the quilt/bag/garment will press the baffles together and effectively form a box baffle.

Why is nobody doing this? Obviously the labor involved is more than that of a traditional sewn-thru baffle, but is it that much more?

re: Does fill power make a difference? Years ago I bought the Montbell Plasma 1000 parka because, well…I thought it was cool.  It is super light and very warm, but honestly I find myself prefering garments that use 800FP.  It’s hard to explain why, but they just feel “cozier”.  Perhaps, psychologically, the slightly heavier “thicker” 800FP jacket feels warmer?

[Jerry Adams]

I looked at Rabb interstitch.  That’s a little different.  For one thing, with “asymmetric baffles” it is sewn through, in that when you’re all done, if a seam were to fail, you can just re-sew it.  There are no seams hidden inside.

I think the asymmetric sewn through is more difficult than regular sewn through because you also have to make the ends longer, so you have to fold the fabric when you’re sewing the seam.  Best to make a square test piece, as I pictured, to figure out how to do it.

Asymmetric sewn through is easier than regular box baffles.  Half as many rows of stitches.  You don’t have to cut a bunch of strips for the baffles.

Yeah, if you put the flat side out then the gaps where there aren’t down are inside so you lose negligible warmth.  I do that for  quilts.  I’ve made three.

Or, if you put the flat side in, and have a jacket on outside, then the air gaps between baffles are covered so no air flows out of it so you lose negligible warmth.  I do that for a vest.  Then the baffles aren’t compressed as much so the down is better allowed to fully loft.  They just hang there, rather than being compressed by the outside layer of the vest.

I made a vest with conventional box baffles which I was not happy with – too short – my first down project.  Then I did a couple vests with asymmetric sewn through and that was a lot easier and just as warm.

[Jerry Adams]

“weight and compression aren’t my main concern, it’s humidity control.
maybe theoretical and  too small of a window of efficacy for me to sense, but my momma said I’m special so it’s prolly right.”

Yeah, previous threads about this – lower fill power down is supposed to handle water better.  More feathers.  It would be interesting to study this more.  It makes sense to me.

And the difference between, for example, 850 and 900 down is un-noticeable.  If you had 10 ounces of down in a project you’d save 1/2 ounce, but I bet one sample of 850 could actually be just as good as a sample of 900.

I recently got some 900 from thru-hiker rather than 850 from RSBTR.  The 850 was treated for one thing, and I preferred the un-treated.

[Weekend Gear Guide]

Thanks Jerry for the explanation. Good design!

Regarding what you mentioned:

Yeah, if you put the flat side out then the gaps where there aren’t down are inside so you lose negligible warmth.  I do that for  quilts.  I’ve made three.

Arc’teryx does something similar with their Firebee AR, but use a square baffle design with the flat side out and the square baffles in and beside each other similar to your strip baffle design, with the same design intention to remove any gaps and thus any loss in warmth.

https://assets.trailspace.com/assets/5/6/0/8799584/IMG_1470.jpg

[Jerry Adams]

yeah, that looks more like asymmetric baffles

[Rex Sanders]

For quilts, would asymmetric sewn through baffles (ASTB) be heavier than box baffles (BB)?

BB: NN ounces of down, encased in 2 layers of nylon roughly the size of the quilt, plus much lighter baffle fabric every few inches.

ASTB: Same weight of down, encased in 1 layer of nylon roughly the size of the quilt, plus one more layer roughly the size of quilt plus twice the baffles.

— Rex

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