How many degrees of warmth are gained from an ounce of overfill?

**Zac.Files** · 03-21-2015, 20:47

I'm in the market for a hammock gear incubator 20 and wondering how many degrees of warmth are gained from an ounce of overstuff. Are overfills worth the money? I do 4 season camping in New England and experience temps in the winter ranging from 10 to low 30s degrees F. Will an overstuff keep me comfortable in lower temps?
Thanks zac.files

**2ply** · 03-21-2015, 21:45

Each additional ounce of down will give you an extra 2- 3 degrees of warmth.

**SilvrSurfr** · 03-21-2015, 21:59

I've heard different estimates. I always thought an ounce of overstuff was worth 5 degrees. So you could turn a 20* UQ into a 10* UQ with 2 oz. of overstuff. However, I was looking at FAQs on HammockGear, and saw this question:

What is the added benefit of overfill and what do the various levels (1-4 oz) translate to in terms of real world performance?

To which Adam replied,

"The overfill is available for those who plan to push the temperatures past the quilt rating. While we rate our quilts generously, some users plan to push the quilt a bit past their limits, but not enough to jump their order to the next available rating. They will opt for an ounce or two of overstuff for extra insurance. Variables prevent us from making it an exact science, however. Caloric intake, clothing, shelter, other insulation, etc. can factor in how much the increase of the temp ratings are with overstuff. For example, an underquilt of a 20*F rating with one ounce of overstuff can be used to 15*F with a solid topquilt, a good shelter (tarp), adequate caloric intake, and a normal body temperature."

http://www.hammockgear.com/frequently-asked/

So that sounds like 10 degrees per oz.

**Boston** · 03-22-2015, 03:51

It depends, but it isn't much. Based on the data available over stuff adds about 0.1 to 0.2*F per percent over stuff. I usually estimate it at 0.15*F/%.

So for 1oz in a standard Incubator 20 with 12oz nominal fill thats an 8.3%over stuff. Expect a temp rating increase of 1.25*F.

Loft is the dominant factor in warmth. If you want a warmer quilt, buy one with more loft. HG will custom make quilts for no extra charge, beyond the down needed to fill them.

The 5*F claim has never been proven, or even really had any evidense presented. I think it's just an estimate that got thrown around so much it began to be taken for fact. And if you think about it a static value like that makes no sense. 1oz add to 5oz or 1oz added to 20oz both have the same effect? I don't think so.

Heres the thread where the available data was analyzed. Lots of discussion too:
https://www.hammockforums.net/forum/...=1#post1352621

**kayak karl** · 03-22-2015, 07:34

go to the zero degree quilt. if it drops to 10, what guarantee do you have that it won't drop to 0. also elevations can play havoc with temps. i use my zero up to 30 and am not hot.

**kayak karl** · 03-22-2015, 07:45

Originally Posted by Boston

So for 1oz in a standard Incubator 20 with 12oz nominal fill thats an 8.3%over stuff. Expect a temp rating increase of 1.25*F.

you stated the 5 degrees has never been proven, so assuming the 1.25 has. if you can increase a quilt from 20 to 21.25 or even 22.5 (which i don't think would even be noticed in the real woods world) then over stuffing is a waste! even maybe a rip-off??

**TallPaul** · 03-22-2015, 07:48

Originally Posted by SilvrSurfr

"...For example, an underquilt of a 20*F rating with one ounce of overstuff can be used to 15*F with a solid topquilt, a good shelter (tarp), adequate caloric intake, and a normal body temperature."

http://www.hammockgear.com/frequently-asked/

So that sounds like 10 degrees per oz.

That reads 5° per ounce to me

**nothermark** · 03-22-2015, 09:16

My impression has long been that overstuffing compensated for loft loss with accumulated dampness and dirt in the down common with extended tripping.

At least part of the problem is the amount of loft is controlled by the shell construction as in baffle height or tube design. if one picks a given thickness and stuffs to just loft to that thickness then use will cause it to thin. OTOH if one adds extra down it compensates for the loss by in lofting power. If one has big down chambers then the added fill will cause rounding between the baffles and add thickness at the cost of width. There are limits to the rounding.

**SilvrSurfr** · 03-22-2015, 10:28

Originally Posted by TallPaul

That reads 5° per ounce to me

Oops.

**Boston** · 03-22-2015, 15:23

Originally Posted by kayak karl

you stated the 5 degrees has never been proven, so assuming the 1.25 has. if you can increase a quilt from 20 to 21.25 or even 22.5 (which i don't think would even be noticed in the real woods world) then over stuffing is a waste! even maybe a rip-off??

It would be from 20*F -> 18.75*F

I wouldn't say proven, but based on analysis of the one, and only, data set specifically looking at the impact of overstuff to warmth that is the result. But that's still more evidence than whats provided for the 5*F claim.

I've long been wondering why the overstuff option exists. I'm an advocate pf having the quilt designed to the correct amount of stuffing to perform correctly - instead of making it user variable. The question then comes into play, "is the standard amount the supplier lists enough?". There are other benefits of overstuff besides warmth, and SOME overstuff is required for good design due to the way down FP is measured - you never see full listed loft in the real world because the down needs to be specially conditioned before the FP measure, plus the impact of compression in real world use.