The effect of "overstuff" on a down quilt?

[sir_n0thing]

With some quilt makers offering an overfill option on their down quilts, I am curious as to the exact effect this may have.
Just an example....
Stormcrow over at Hammockgear.com offers up to 4oz overfill on his winter quilts.
On your average quilt, does the extra down equate to increased loft? Or better insulation at the same loft level as the base fill level?

I'm shopping for a winter quilt, and just trying to make sure I understand the facts before I start peeling off the Benjamins!

[angrysparrow]

On your average quilt, does the extra down equate to increased loft? Or better insulation at the same loft level as the base fill level?

On a quilt with properly sized baffles, it doesn't create more loft, but it does loft faster when uncompressed since there is more down expanding to fill the space. Which, as you might guess is also warmer, but creates a more dense insulation fill. That increased density is less susceptible to outside convective forces (think a side breeze).

IMO, overstuff is money well spent as long as the baffles are well designed and it's not 'overdone' past the point of diminishing returns.

[Nighthauk]

So angry sparrow is there a quantifiable degree difference per oz of overstuffed. I know it varies per person but on average. I just ordered and impatiently waiting for a UQ from you guys. I ordered it with 2 oz extra. What would you say that the range is extend by?

[angrysparrow]

So angry sparrow is there a quantifiable degree difference per oz of overstuffed. I know it varies per person but on average. I just ordered and impatiently waiting for a UQ from you guys. I ordered it with 2 oz extra. What would you say that the range is extend by?

The quantifiable amount will vary based on the amount of down, the size of the baffles, the length of the quilt, etc. A better way to think of it rather than by weight is in percentage of overstuff by volume.

For instance, if a given amount of down (1 oz) is specified to fill a certain amount of baffle space¹, then overstuffing that same space with 1.2oz of down instead of 1oz is 20% overstuff. Given a LOT of various factors that can influence how much warmth that will add, I'd say an addition of 10ºF is not overstating the improvement that 20% would add and sometimes a bit more. But to my mind more importantly, the density increase is yields more practical results in the field, as the quilt is more tolerant of breezes and other convective action.

I've not seen or read much 'official' science by any of the manufacturers here about overstuff percentages and the point of diminishing returns, but I do know that at least two of them have done some testing. As I recall, at least one found that between 20% and 25% overstuff is about where the cut off seems to exist in the dollars vs warmth ratio.

Each manufacturer will rate it differently, of course, given varying baffle sizes, fill power of down, length of quilt, etc. And I'd trust each of them to do the math on their own gear. But all my field experience with a variety of quilts (more than a few) suggests that overfill is usually worth it, especially in windy conditions.

YMMV of course...just sharing my view.

¹ - The amount of space occupied by 1oz of down varies by the fill power rating of the down.

[Nighthauk]

I concur. :-)
Serious though thank you. I expected it to be something like that.

[sir_n0thing]

Excellent information! Thanks much for that.
I am leaning towards adding a couple of ounces of overfill being worth the extra cash...

[MAD777]

I have been meaning to start a discussion along these lines, so now is as good a time as any.

Bear with me a minute while I propose a new way of thinking about "overstuffing."
I propose that there is no such thing as overstuffing down. It is actually undersizing baffles.

I decide what temperature I want to achieve and determine how much loft is needed.
Then, I multiply the loft times the length and width of the quilt and finally divide by the fill power of the down I'm using. That gives me the ounces of down I need.

So, let's say I want a quilt with "X" inches of loft. Now I determine how short the baffles need to be to tame the down so that it doesn't all wander off to one side of the quilt. The extreme case would be a sewn through quilt - zero height of baffles. However, that gives cold spots.

So, where is the happy medium between cold spots and down control?
For my quilts I use 2/3 of the loft I was looking for, but never more than 1" less.
A couple of examples: for 2" of loft I make the baffles 1.33" high (2/3rd's)
for 4.5" of loft I make the baffles 3.5" high (1" less).

My logic for limiting the baffle height to 1" less than the loft is that 1" of loft makes 10-12 degrees difference in temperature. That's about as much temperature difference across the quilt that I'm willing to accept. (This is personal opinion only and holds no significance other than that).


BTW, I use a formula that I got by performing a linear regression of Western Mountaineering's tables.

temp = 56.7 - (11.64 * loft) or
loft = (56.7 - temp) / 11.64

WM is one of the most respected sleeping bag manufacturers and is famous for not lying about their temperature rating. They make premium bags for a premium price. I know, I own two of them.

To me, this upside down way of looking at this subject is easier to follow. The average loft is what is going to keep you warm. Tests have been done in recent years by Richard Nisley (a research scientist in the Bay Area) that show that down can be compressed almost 2.5 times it's free loft and maintain the same insulation properties. Basically, the increase in conductive losses are cancelled out by the decrease in convective losses.

[angrysparrow]

Bear with me a minute while I propose a new way of thinking about "overstuffing."
I propose that there is no such thing as overstuffing down. It is actually undersizing baffles.

That's practical advice for sizing baffles on DIY projects. I'm sure some of the manufacturers here used that very method for calculating the baffle sizes and fill amounts of their quilt models.

But I think the term overstuff really does apply, especially to a situation like the OP mentioned. He's looking at a quilt with set dimensions (including length and width of baffles). While the manufacturer might offer to put more down into their pre-set shell pattern at request, it's unlikely that they will resize the baffles to a specific amount of down just for the one quilt.

[sir_n0thing]

Ahhh, so in that example, it would be like asking a quilt maker to use a smaller baffle size with the same amount of down...

[Buffalo Skipper]

I am a little confused her (and very underinfomed). So if I order an XYZ full length underquilt rated to 20°, and I get it with 1 oz of overstuff, it will:
1) weigh 1 oz more
2) theoretically provide better draft protection (from a breeze)
3) possibly reduce the rating of the quilt by maybe 1° or 2°

Is that right? Keep the answer simple. I am really burned out at work and cannot think in big words right now.