Overfill vs a lower temp rated bag

[westsloper]

I’ve been educating myself on quilts, and the sense I’m getting in regard to overfill is that it is an important feature. This is partly because a bag that isn’t overfilled will only fully loft under ideal conditions (from what I understand). The other reason is to keep down from shifting and creating cold spots (unless you find down shifting to be a desirable feature).

I know several manufacturers do 30 percent overfill standard (I think this applies to El Coyote, UGQ, EE). Some (like Gryphon Gear) go even higher. Others offer it only as an add on for extra money or not at all.

The owner of Zenbivy stated that he doesn’t do overfill and doesn’t like the concept - he simply recommends going down a step in terms of temperature ratings if you want more insulation. That seems logical enough to me, although it won’t necessarily prevent down shifting.

Still, I’m not sure I understand the difference between the two choices and all the trade offs at play when discussing something like a 10 degree bag with no overfill and a 20 degree bag with 30 percent or more. Any insights?

 

[ljalberta]

I’ve spent way too much time trying to break up clumped down and migrate down to fill cold spots to ever purchase a bag or quilt without overfill again.

Just my experience.

 

[AZ_Hunter_2000]

No experience with Gryphon but their literature states that their quilts are pre-overfilled. They use the “original” down and their “overfill” down to get to the published temperature rating. That’s not “overfill” to me; that’s what it comes with by design.

Others have a published temperature rating and then offers an overfill option. That is more honest.

But don’t expect a massive improvement in warmth. For sleeping bags the expected improvement is only 5-10 degrees. It’s a nice buffer but it’s not going to make your 40* bag a 0* bag.

 

[sneaky]

Yes, these "30% overfill" claims are just marketing. If that's how much fill you intended to put in that quilt or bag it isn't overfilled, it's just properly filled. Overfill is when you take a properly rated bag/ quilt and then give the customer the option of adding more down e.g. Western Mountaineering bags.

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[Kevin Dill]

Adding overfill insulation is definitely NOT an automatic big improvement in warmth. Any bag or quilt achieves its temp rating by accomplishing loft (measured in inches or cm) and creation of dead air space. It's the loft and dead air that allows your body heat to stay in place. A bag, quilt or garment can only loft as much or far as its construction allows. A bag built and filled to loft 6 inches will in all likelihood not loft to 9 inches if you add 50% more fill. That's an extreme example of course, but it holds true with lesser amounts of overfill....again....depending on a bag's construction. You might add 20% overfill with the result being simply to compress and force more insulation into a defined space, with no real gain in R-value. For overfill to work, it has to increase measured loft and/or dead air space.

I'm not against overfill. I have a WM Sequoia with a couple extra ounces of down. I can't prove it does a thing beyond the bag's temp rating. I tend to think the overfill helps ensure the bag will achieve its maximum loft and actual temp rating, especially as years pass and goose down degrades some from repeated use.

Finally, I don't know of a single study or test of overfill(ed) vs 'normal' bags which proves a serious benefit to warmth. I'd love to see it done. Personally i think the smart money is on buying the right bag - right rating and go with it, versus guessing at the benefit of overfill.

 

[Muledeerfanatic]

UGQ quilts are stuffed full compared to others
I have a 20 degree with 2 oz overstuff in the feet and it is like a 10 degree
My HG 20 with overstuff is more of a 30 and I am a very warm sleeper. All the down migrates to the sides where it does nothing

 

[BRTreedogs]

The reason people want over fill is if your down is bunched and you hold your bag up to light you will see bare spots. Aka a cold spot.

The baffles in a lower degree bag are larger creating more dead air insulation space.

So over full may eliminate some cold spots but the larger baffles make it a warmer product.

If you're diligent about making sure your down is bunched over fill is a waist of weight so to speak, because your not adding warmth compared to a fully lofted baffle.
Your basically making it easier to use by adding weight.

 

[tdot]

In its most basic form, the difference between overfill and a lower temp rating is typically the height of the baffle. 20oz of down in a 5" baffle will not be as warm as 20oz in a 6" baffle.

Personally I've found the concept of overfill to really only relate within a single manufacturers lineup. Properly comparing one manufacturers volume of down fill to another manufacturers down fill can be difficult at best. 20oz in one bag doesn't related to 20oz in another mfg's bag. The cut is different, baffle heights and spacing are different, etc. This all changes how that 20oz of down is utilized to fill the bag.

 

[sneaky]

Yep, people confuse overkill with loft. Loft is the true measure of warmth retention, that combined with the cut of the quilt or bag. Some of the claims I see going from manufacturer to manufacturer are rather dubious at best.

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