# Optimum baffle width?

• 09-21-2010, 11:26
jbo_c
Optimum baffle width?
Is there an optimum baffle width? Is 8 inches OK? 10?

Is it related to baffle height? Is a wider baffle OK for shorter baffle height?

I'm just beginning to seriously consider making a down UQ.
• 09-21-2010, 11:44
warbonnetguy
optimum width would depend on thickness, the thicker the quilt, the wider the baffles could be, the thinner it is the narrower they will need to be

look at sleeping bags, not many out there with wider than 6" on a 3 season or winter SB.
diy people have used wider baffles to save sewing time, but i can't say how that's worked.

the manufactuers that i know of that have used really wide baffles in the past ended up making them narrower eventually
• 09-21-2010, 11:50
Dutch
I like things to divide out neatly. So 48" wide is screaming for 6" apart. I tried to go narrower than 4 inches and I had a very hard time filling it. So I think 4.5" to 6" works best for me.
• 09-21-2010, 20:25
Two problems develop when the spacing is too large for the baffle height.

1. If filled to the theoretical full volume by multiplying the baffle height times the spacing width, and then the top & bottom fabric balloons, that creates more volume in the resulting space. Therefore, the down can randomly migrate leaving clumps and voids.

2. One can overfill the baffle space to avoid number 1 above, but then the outside fabrics really balloon up, resulting in an overall shrinkage of the finished product. This is because the outside fabric resembles waves on the ocean and your baffles have had to move closer together. So, your garment material must be made longer to compensate for this affect.

The mathematical "perfect" baffle spacing can be determined as follows: subtract 2 from pi and then multiply by the baffle height.
Spacing = (pi - 2) * Height

There's a lot of geometry that goes into that but the bottom line is this. If you use this formula, the volume calculated by multiplying the rectangular height times the spacing, is exactly the same volume as if you assume you've overstuffed the baffle to the gills and each one is perfectly round on top and bottom (two semi-circles) plus the rectangular space between the two baffles.

With this spacing, there is no tendency for the baffles to puff up (no matter how much they are overfilled) because the volume in the "puffed up" state is the same as in the "flat" state.

Of course practicality comes into play here, particularly with thin quilts. You had better really like to sew, because the baffle spacing on a thin quilt is going to be awfully small.

Just remember, the wider your baffle spacing is in relation to the height of baffles, the more migration you will have, unless you overstuff. I you overstuff, you will have shrinkage to account for, so your piece needs to be larger overall (which means more sewing - you can't win!!)

I simply stay as close to the above formula as I am willing to sew ;)
• 09-21-2010, 22:06
jbo_c
Not to be a wisea\$\$ but isn't (pi-2)=1.14? Why not just say 1.14 xbaffle height? or was that so the engineers would know what you were doing?

That logic makes perfect sense. But isn't the net result very close to "square is the optimum baffle width"?

Thanks.

Jbo

My next question is, what's the difference between "overstuffing" and just making the baffle taller to begin with as far as insulating ability?
• 09-21-2010, 22:19
angrysparrow
Quote:

Originally Posted by jbo_c
My next question is, what's the difference between "overstuffing" and just making the baffle taller to begin with as far as insulating ability?

Higher densities are more resistant to loss through convection.

If you take 2 quilts, each with the same amount of down, but one is the 'normal' baffle height for its amount of fill and the other a shorter baffle but overstuffed for its height.. The one that is overstuffed is more resistant to heat loss when it is subject to wind blowing across its surface.

At least that's my own observation through using several quilts and comparing the fill vs warmth.

There of course has to be an optimal overstuff percentage, where adding more down doesn't yield as much benefit as increasing the baffle height, but I don't know what that percentage might be. In any case overstuffing must be accounted for in the dimension specs, or you end up with the #2 problem described by Mad777 above.