Over Stuffing vs Temp Rating

[scrope]

Speaking about baffle height, I did a DIY UQ and, because I had a bunch of down left over, I just stuffed it into the quilt. It was actually quite a lot. So what happened is that instead of getting rectangular-ish baffle chambers, I got these very oblong chambers because the top and bottom fabric was much softer and malleable than the baffle material. The quilt was much narrower than I intended (at least at rest).

The reason people dislike sewn through quilts is because there isn't any real insulation at the seams. With baffles, you have a similar situation where, at the baffle, you only get the insulation of the baffle height. In my situation I think I had 2" baffles so around the baffles it was only a 2" level of protection but in the center of the chamber it was more like 4" which would make the center much warmer but it wasn't going to do anything the temperature around those baffles.

[scrope]

I think that the down in a baffle does two things. First, it loft the baffle to its height, and you need enough down to do that. Secondly, the down prevents air from moving around inside the baffle. Cold air on the outer side of the baffle, warm air on the body side, and you don't want it mixing. "Air, stay there." Too much down gives surface area for the cold to migrate. So, the perfect amount of down is that which maintains the loft, stops air from moving inside the baffle and presents the least surface area. And then add humidity problems which reduces loft and give cold an easier path to travel...

That sounds right to me. If you add more down you are adding more weight. If it helps fluff up the quilt more and keeps the air movement the same you should get more warmth. If it doesn't fluff up the quilt more and the air movement is the same, I don't see how adding that down made the quilt any warmer. Although if all the down collapses a bit because of dampness I would think the added down might prevent the down from de-fluffing and retain the temperature rating. And as you point out, there should be a point where you have so much down packed so tightly that you give a conduit for the cold to pass through the quilt.

[Just Bill]

I recall reading about this too, if I recall the conclusion I read was something like "you can compress the down something like 40+% with no loss of warmth". If that is true it says to me that if the fill amount stays the same while baffle height is shortened by say 30% (partial compression)... nothing happens to the temp rating. That implies to me that overstuff does actually add warmth because...

If you can indeed compress by 30-40% and not lose any warmth then that would mean you could take a "regular stuffed" quilt with a 3" baffle height (say 3", 0 deg and 16oz down) and shorten the baffles to 2" (but use the same 16oz fill wt).... So same amount of down just 33% compressed by using a shorter 2" baffle instead of 3"... and it should result in no change to the temp rating (0deg). So you're still getting the same 0deg rating from 16oz of down regardless of wether the baffle height is 2" vs 3", because the 33% reduction in baffle height is not "enough" compression to reduce the warmth of the 16oz of down and so the rating doesn't change.

That would mean that you can take a 2"/12oz fill/20deg quilt, and simply overstuff it to match the 0deg fill weight (16oz) to make a 2" zero deg quilt, because as long as you don't go over 40% compression(or whatever the limit is) then 2" vs 3" baffle height would be irrelevant to the temp rating because it isn't enough compression to have any effect...That leaves the fill amount as what largely determines the rating.

I feel like there is a fair amount of leeway in regard to baffle height and I can pretty much guarantee if you got all manufactuers to tell you their 20deg baffle height they won't all be the same... even though they may all be accurately rated at 20 deg. However, manufactuers making very similar sized products (50" wide x 72" long topquilts with a taper for instance) will often have strikingly similar fill amounts for any given rating, and this is no coincidence, fill amount is the major factor effecting temp rating, not baffle height which can and does vary from shop to shop. Also companies making a quilt in 5 or 6 different temp ratings are not all using 5 or 6 different baffle heights...Some may so but some do not...some use the same baffle height for 2 different ratings and just adjust the fill weight, and nobody to my knowledge lists the actual baffle wall height anymore because most customers give it way to much importance while in reality the exact baffle height for a given temp rating is probably one of the least important factors and shouldn't even be considered by anyone other than the designer.

So I know I am talking about baffle height alot here, but for anybody that is confused, slight compression and reduced baffle height are the same thing. If you can compress the down to a signifigant degree without losing warmth, then you can overstuff to a signifigant degree, putting say a 0deg winter fill amount in a 20 deg sized shell without losing the 0deg rating because yes, you are overstuffing/compressing but not enough to have an effect. So if 16oz makes your 3" quilt 0deg then 16oz should give you the same 0 deg rating if adjusted down to a 2" baffle wall height.

This is all dependent on that origional premise being true, but I believe that it is, and as long as you don't overstuff (compress) too much you will find that more down equals a warmer quilt while the baffle height can fluctuate some without any negative effects at all. I think going with too short a baffle obviously can cause too much compression and reduce the warmth while too tall a baffle results in the down being able to move way too easily resulting in more thin/dead spots which also reduces warmth, but the sweet spot (correct baffle height) can vary by a reasonable amount without any effect, So if two manufactuers have 2 exactly same sized items with the exact same fill amount you can bet the temp rating will be the same while baffle height may not be. I have done this (put a winter fill amount in a 20deg shell) and it results in a winter quilt.

Jerry Adams had a unique quilt design that I got hung up on for a bit. It basically was a zero baffle quilt. You increase the width of the outer shell so that you can sew a series of half circles. The appeal was simplicity of construction. It also allowed you to not get too hung up on differential cutting on complex shapes like bridge bodies. Anywho...

Jerry Adams baffle.pngJerry Adams baffle 2.png

Not sure how many other folks actually built these, but the experiment led me to some insights that I shared there and here at some point.

I think the issue is as much 'container vs contents'. I agree with you generally on what you are saying above Brandon... within limits. Too much down (especially in SUL shells) will deform the shell itself. If there is nothing to resist the down's push to expand it will eventually deform a rectangular baffle into a circle. That was one reason I never put much stock in that density decrease idea shared at BPL. In a fixed size container like a plexiglass tube; you could truly achieve a higher density in a fixed area to test. In a soft shell- you'd have an impossible time maintaining that density.

Anyone who has built a down product that was say 50" wide on paper (or unfilled) has seen this happen when they find that the finished product is an inch or more narrower than planned. As you point out- even with dead nuts 2" baffles used... the actual loft of the product would be higher. This was one of the purported advantages of the Jerry Adams quilt. The inner shell was locked in place while the outer shell of half circles could expand.

I think some of your products (and UQ's generally) have some advantage over a top quilt in this regard as they are under some tension in several directions. I haven't seen one in person but basically your Wookie is a good example of what Jerry Adams was shooting for... your inner layer is "shape stabilized" under tension and the down is free to expand (loft) away from the user without excessive losses in the length and width.

So to tie things back; That may be the reason that overstuff may be a trend mainly unique to hammock's, and specifically to underquilts. The tension of the underquilt may allow a density increase one couldn't achieve in a top quilt. If you drastically overfill a top quilt... all you get is a really thick quilt several inches narrower than you planned. (and ultimately a heavier one too)

I do agree that the actual baffle height used is not ultra critical. So long as you can design your shell to distribute the down properly across the area of quilt you're covering... the down will sort itself out.

This is the summary I shared before-
Overstuff Insight.pdf

For non nerds- the two pictures are helpful to illustrate how a baffle goes from a simple rectangle to a football shape with the tips chopped off.
That results in a roughly 25% increase in area and a roughly 1/8" per baffle loss in overall width.
So your average 30% increase is actually 25% in actual fill with 5% of overstuff for real world losses and ensuring no cold spots.

To further back up the point Brandon is making on baffle height: Overstuff Insight.pdf
Generally we are talking roughly 1/4-3/8" of loft per 10* difference, growing to 1/2" as you approach zero (non-linear increase).
Either way... nearly every vendor I've ever seen ends up with a quilt that lofts a bit higher than listed. Regardless of baffle height- average loft ends up about the same across the board.
(Worth noting... this is about the only chart that shows a different loft for UQ use- something I suspect many vendors know but is not often shared or discussed).


End of the day...
You can still mess up the math as a vendor, or come up with your own weird version of calculating error and correction.
Generally I find that each vendor plays with their own version of XX% to compensate for their product design or measurement method.

For customers though...
When you ask a vendor to overfill a malleable shell; they may not be able to predict or advise you on how that will change the geometry of the quilt.
But if it works for you... do you care?
And if the vendor offers it, they've probably done it enough to find out that at the very least... enough people haven't bitched about it not working out. So that they can continue to offer it without harming their reputation. If the customer is happy... who are they to argue, lol.

In the case of underquilts... maybe I am over emphasizing this issue and you may indeed gain benefits.
With the quilt under tension, and shell materials closer to 1 oz per yard than .05 oz per yard then you may indeed see density increases similar to lab tests as the shell is more rigid than an unconstrained quilt.

Either way... this is really a true nerd discussion. And then only really a gram weenie one.

The end goal is to achieve a given temp rating.

If there is an art to discuss; it's doing that with the bare minimum of materials.
However we have mainly reached a point in general gear design and materials that we may be getting silly too. The overall weight and performance of gear is 10 or 20 times better than a decade or two ago, and even in the last few years the increases have been large on that front. To a large extent- everyone is making pretty amazing gear on the top end.

And on the budget end... it's pretty darn close to bleeding edge SUL gear levels of quality we saw only 5 or 10 years ago.
So overall it may be a moot point of discussion as you can't really go wrong.

[Just Bill]

Speaking about baffle height, I did a DIY UQ and, because I had a bunch of down left over, I just stuffed it into the quilt. It was actually quite a lot. So what happened is that instead of getting rectangular-ish baffle chambers, I got these very oblong chambers because the top and bottom fabric was much softer and malleable than the baffle material. The quilt was much narrower than I intended (at least at rest).

The reason people dislike sewn through quilts is because there isn't any real insulation at the seams. With baffles, you have a similar situation where, at the baffle, you only get the insulation of the baffle height. In my situation I think I had 2" baffles so around the baffles it was only a 2" level of protection but in the center of the chamber it was more like 4" which would make the center much warmer but it wasn't going to do anything the temperature around those baffles.

Besides my last post above-
I'm a carpenter. Building science and insulation is a hot topic.

A traditional stud wall has insulation only between the studs. (basically a sewn through quilt)
Something you can actually see in a home's roof easily enough- https://mycozyhome.com/2016/12/roof-...s-reveal-much/


An advanced wall has a layer of foam applied to the exterior. So while there is not 'full depth' insulation at each stud. There is a thermal break and some insulation there.
This is basically a baffled quilt. Even in a low loft quilt (50*) choosing baffles over sewn through eliminates most of the thermal bridging and provides an overall higher average loft.

To Brandon's point... a recent innovation is higher density batt insulation- a typical 2x4 wall gets an R-13 batt. But there is a high density version that gives R-15 in the same cavity.
Spray foams and other products can also increase the R value based upon this 'low loft' theory.

Generally speaking though- reduced thermal bridging and overall higher 'average insulation' is winning the debate. Some advanced framing walls move nearly all the insulation to the exterior using various foams and stand off systems to attach exterior cladding (siding, etc). Because there is less variation within the system- there is less air movement that results and causes more issues. (like moisture in walls)

In terms of applying that to a quilt... the lesson would be to achieve the most uniform coverage possible. So while that 2" baffle/4" peak loft combo will deliver an average of 3"(depending on baffle spacing) ... you're probably still best off achieving that average 3" loft with 2-7/8" baffles and 3-1/8" peak loft.

Unlike a building- where increasing stud spacing increases insulation space... Increasing baffle spacing tends to increase deformity of the shell. (the baffle to peak loft ratio gets more out of whack).
Just like in a building... these fluctuations in insulation level may encourage mirco climates (drafts) and increased air movement and draw humidity into the quilt.
Overall- what you want is uniform dead air. High's and low's encourage air/heat flow and reduce insulating ability.

Just like in a building... too many weak points and it doesn't matter how heavily you insulate the rest. You can blow Insulation into your attic until is flows out the ridge.. but if your windows are junk it won't matter on your heat bill.
The larger the thermal gradient (difference in ambient temp vs conditioned temp) then the greater these weak points affect things.
That's why sewn through shells in quilts are generally relegated to summer only gear; the gradient isn't so large that it becomes an issue. Somewhere around 35* though... having that little grid of zero insulation sewn lines is enough loss to overcome the warm strips between them and cause the quilt to 'fail'.

[scrope]

Thanks for the detailed explanation JustBill. It pretty much fits with my empirical observations based on my own DIY TQ and UQ.

If you took that 5" x 2" baffle by itself and had enough down to push against all the sides equally without other forces acting on it the result would be a 15" circumference circle which has an area of 15.6" which is considerably more than the 10" area if the baffle remained a rectangle. The diagram in the Overstuff Insight document seems pretty accurate to me since the sides of the baffle don't seem to change much but it's the deformation of the top and bottom mostly changes the shape.

This topic isn't as simple as one might think because we tend to make (often invalid) assumptions -- such as the baffles are rectangular. Even with a differential cut I was surprised at how much the quilt deformed from my expected shape. Since I haven't heard anybody with a solution to keep the baffles rectangular we must confront the reality of non-rectangular baffles.

I like your suggestion that what is often called over-stuff is just the additional down needed to fill the actual shape the baffle takes when filled.

I also like your idea that the most important aspect of a quilt is what's the temperature that it can keep you warm to. If a 40* quilt keeps you warm to 0*, we should probably consider it a 0* quilt. And since people are different (I sleep very cold) every individual needs to determine what quilt rating is appropriate for them.

I'm planning to make a TQ/UQ set for warmer weather since my "over-stuffing" my 0* quilt made it more like a -15* and huge. This has given me a lot to think about when designing my next quilts.

Thank you all so much to everyone who has contributed to my better understanding in this thread.

[Just Bill]

OS insight 2.png

Didn't post it earlier- but someone asked for this before. Just a visual way to represent what you're saying. (The jerry adams baffle on the left, the rectangle on the right).

If you built a baffle out of plexiglass or something rigid...
Then all we would need is perfect fill (8 in sq). If we added the typical 30% overfill... we'd have 30% over stuff right off the bat.

In fabric-
Perfect fill would allow it to maintain a rough rectangle due to the seams/stitching. rectangle worth of area... at standard density.
Standard overfill would deform the baffle as shown above... so same density, different area.
However if you kept going (in isolation) you'd need roughly 42% overfill the fabric rectangle to 'perfect fill' since the rectangle deforms to a circle(11.33/8).

From there, any extra fill (overstuff) would then increase density.

Good stuff for MYOG or quilt designers to consider. Perfect fill, overfill, and actual overstuff (increase in density).

For folks who are simply buying gear... all the research needed is to find a good vendor and trust them to do the job.

[BillyBob58]

I recall reading about this too, if I recall the conclusion I read was something like "you can compress the down something like 40+% with no loss of warmth". If that is true it says to me that if the fill amount stays the same while baffle height is shortened by say 30% (partial compression)... nothing happens to the temp rating. That implies to me that overstuff does actually add warmth because...

If you can indeed compress by 30-40% and not lose any warmth then that would mean you could take a "regular stuffed" quilt with a 3" baffle height (say 3", 0 deg and 16oz down) and shorten the baffles to 2" (but use the same 16oz fill wt).... So same amount of down just 33% compressed by using a shorter 2" baffle instead of 3"... and it should result in no change to the temp rating (0deg). So you're still getting the same 0deg rating from 16oz of down regardless of wether the baffle height is 2" vs 3", because the 33% reduction in baffle height is not "enough" compression to reduce the warmth of the 16oz of down and so the rating doesn't change.

That would mean that you can take a 2"/12oz fill/20deg quilt, and simply overstuff it to match the 0deg fill weight (16oz) to make a 2" zero deg quilt, because as long as you don't go over 40% compression(or whatever the limit is) then 2" vs 3" baffle height would be irrelevant to the temp rating because it isn't enough compression to have any effect...That leaves the fill amount as what largely determines the rating.

I feel like there is a fair amount of leeway in regard to baffle height and I can pretty much guarantee if you got all manufactuers to tell you their 20deg baffle height they won't all be the same... even though they may all be accurately rated at 20 deg. However, manufactuers making very similar sized products (50" wide x 72" long topquilts with a taper for instance) will often have strikingly similar fill amounts for any given rating, and this is no coincidence, fill amount is the major factor effecting temp rating, not baffle height which can and does vary from shop to shop. Also companies making a quilt in 5 or 6 different temp ratings are not all using 5 or 6 different baffle heights...Some may so but some do not...some use the same baffle height for 2 different ratings and just adjust the fill weight, and nobody to my knowledge lists the actual baffle wall height anymore because most customers give it way to much importance while in reality the exact baffle height for a given temp rating is probably one of the least important factors and shouldn't even be considered by anyone other than the designer.

So I know I am talking about baffle height alot here, but for anybody that is confused, slight compression and reduced baffle height are the same thing. If you can compress the down to a signifigant degree without losing warmth, then you can overstuff to a signifigant degree, putting say a 0deg winter fill amount in a 20 deg sized shell without losing the 0deg rating because yes, you are overstuffing/compressing but not enough to have an effect. So if 16oz makes your 3" quilt 0deg then 16oz should give you the same 0 deg rating if adjusted down to a 2" baffle wall height.

This is all dependent on that origional premise being true, but I believe that it is, and as long as you don't overstuff (compress) too much you will find that more down equals a warmer quilt while the baffle height can fluctuate some without any negative effects at all. I think going with too short a baffle obviously can cause too much compression and reduce the warmth while too tall a baffle results in the down being able to move way too easily resulting in more thin/dead spots which also reduces warmth, but the sweet spot (correct baffle height) can vary by a reasonable amount without any effect, So if two manufactuers have 2 exactly same sized items with the exact same fill amount you can bet the temp rating will be the same while baffle height may not be. I have done this (put a winter fill amount in a 20deg shell) and it results in a winter quilt.

Does all of that partially explain why Climashield Apex and older XP insulation (assuming all drafts well blocked of course) has a 20*F rating at just 1.2" loft? And this rating is probably correct for some folks, as your old CS XP Yeti was rated at some where close to zero F, better than that per Cannibal's tests- and with all 4 layers of 2.5 OSY CS only had 2.5" of loft. Clearly, no down UQ could be used at those temps with so little loft. So it seems with down, if we increase the density we can increase the loft. Is CS denser than down, and if so is that part of why it is warmer per unit thickness?
http://thru-hiker.com/materials/insulation.php

http://www.thru-hiker.com/x/index.ph...viewthread/25/

Or compare two of my own kits: the Maxima and the Whitney. These are equivalent jackets, the Maxima being the synthetic version of the Whitney. They are both about the same warmth too: over three years use with the Whitney and two for the Maxima they’re comfortable for me in the 30’s just sitting around. The Maxima has a 3.0 oz basis weight layer of PL Sport with a single layer loft of 0.6” (clo: 3.0 * 0.74=2.2) while the Whitney fully lofted has on average about 1.5” of single layer loft. In other words, the synthetic jacket is as warm as the twice as lofty down jacket.

[OneClick]

We're over-analyzing things on a BPL level now...or worse!

[Just Bill]

We're over-analyzing things on a BPL level now...or worse!

Good stuff for MYOG or quilt designers to consider. Perfect fill, overfill, and actual overstuff (increase in density).

For folks who are simply buying gear... all the research needed is to find a good vendor and trust them to do the job.

For what it's worth; while the magic seems to be gone over at BPL. There was a time where that site was one of the most important around. There are likely a dozen or more companies that would not exist today without it.
Though I agree that over-analysis isn't always a good or healthy thing.

Speaking of...

[OneClick]

Though I agree that over-analysis isn't always a good or healthy thing.

I'm OK with it to an extent and it's expected with any hobby/forum. But after a while it gets out of control.

Not bashing this thread, because it is an important part of hanging. Underquilts will always be one of the most important piece of gear.