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The original was posted on /r/Ultralight by /u/pretzlstyle on 2024-11-24 07:35:21+00:00.

I’m trying to compare the Zpacks Twin Quilt and the EE Accomplice for a prospective thru-hike with my partner. I know that Zpacks has a bad reputation for rating their quilts by limit. I hear the same about EE though. EE claims that their ratings are limits:

Our temperature ratings most closely correspond to limit temperatures as defined by EN 13537/ISO 23537 standards

But I can’t find a similar statement one way or the other from Zpacks.

There are a few old threads about this exact comparison, but info is pretty lacking. Here is a comparison between the Twin, and a custom Accomplice, which matches it’s specs as closely as possible.

So 4.56 oz out of the 5.2 oz difference is accounted for by the difference in down, and 0.64 oz is whatever else. That could either be caused by a difference in geometry, or a difference in warmth, or both. The Twin has a tapered shape, while the Accomplice does not, for example, though the Twin is 2 inches longer. What I want to find out is if any factors other than a warmth discrepancy can explain this.

Loft-implied down content

For a target loft of 2.5 in (which corresponds to the stated ratings of 20 F), we should expect

• (2.5 in)/(900 in3 / oz) = 0.0028 oz of down per in2 of surface area for 900 fill power down for Zpacks
• (2.5 in)/(950 in2 / oz) = 0.0026 oz of down per in2 of surface area for 950 fill power for EE

If the down is equally distributed across the quilt, then multiplying this value by the quilt surface area should match the stated amount of total fill.

The Twin claims a length of 74 in. However, they claim a width of 86 in at the shoulder, and 71 in at the foot. Which is obviously wrong… maybe these are the dimensions of the “open” quilt before sewing the footbox? Looking at the relative quilt dimensions in their photos, this seems to probably be true… so I’ll just half the measurements. The footbox looks to be about 70% of the way down the quilt, and so with a closed width of 43 in from the hips to the shoulders, and a closed width of 35.5 in at the foot, the actual surface area is a rectangle plus a trapezoid;

• [(74)*0.7 * (43)] + [(74 in)*0.3 * (43+35.5)/2] = 3099 in2 = 21.52 ft2 actual dimensions for Zpacks

EE provides a length of 72 in, and a circumference of 86 in. We can assume that this circumference is also just the width of the open quilt. It does not taper. The surface area of the closed quilt is then

• 72 * 43 = 3096 in2 = 21.5 ft2 actual dimensions for EE

The implied fill per each side of the quilt (top and bottom) is then

• (3099 in2 ) * (0.0028 oz/in2 ) = 8.677 oz per side ⇒ 17.35 oz for Zpacks
• (3096 in2 ) * (0.0026 oz/in2 ) = 8.50 oz per side ⇒ 17.00 oz for EE

Actual down content

So both quilts are over-spec for the amount of down that they have. In other words, they are both either loftier than 2.5 in, or they are overstuffed. It’s probably a combination of the two, but the loft is limited to some degree by the baffles, and overstuffing is pretty standard practice for quilt longevity. Zpacks states on the product page:

Each compartment is overstuffed with 30% more 900 Fill Power DownTek water resistant goose down than is necessary for maximum loft to account for any future down compression.

And EE stated in this blog post:

In 2019, we’re moving from our previous 10% overstuff to a 30% overstuff across the board on all our down quilts and sleeping bags.

So the estimated overstuffed weights should be something like

• 17.35 oz * 1.3 = 22.5 oz for Zpacks
• 17.00 * 1.3 = 22.1 oz for EE

However, if overstuffing accounted for all of the weight discrepancy, the overstuff fractions are more like

• 20.30 / 17.35 = 1.17 for Zpacks
• 24.86 oz / 17.00 oz = 1.46 for EE

Conclusion

The conclusion is that (if what I’ve done is at all coherent)

• Zpacks claims 30% overstuff, when they actually provide 17%
• EE claims 30%, when they actually provide 46%

Or the provided down weights are incorrect. I sort of doubt this. Does Zpacks have an incentive to under-report the amount of fill? They love their grams. Does EE have an incentive to over-report the amount of fill? They have faced temperature rating backlash in the past… But I think these are unnecessary assumptions; those motivations also perfectly explain the case that the numbers are correct.

In summary, they do both provide 2.5" of loft, or whatever the max allowable loft by the baffles are, when new. So when new, they should be comparable in warmth. But EE should have more longevity after cycles of down compression.

So what should I (or you) do?

• if we treat our quilt gently and never use stuff sacks, maybe the longevity consideration diminished and we can go with ZPacks. Is that even true though? Probably not. But this post is already long enough, so I’ll leave it for another time
• if we don’t actually intend to use the quilt at 20F, but will instead use it at 30F and above, maybe the lacking longevity of the Zpacks is acceptable. We will just have to be aware that clothing supplementation of the sleep system may need to increase over time.
• if we don’t care about 5.2 oz, or we think that 5.2 oz is worth extra longevity, then obviously go with EE

For me, I already use clothing to supplement my sleep systems, and I’m an insufferable gram-counter. So I may go with ZPacks for that reason.

Caveats

Let me stress that I am not claiming to have discovered the actual overstuff ratios that these companies are using, and I should be careful about accusing ZPacks of anything. In fact, I assume that overstuff is a fairly simple thing to just do correctly, if you’re sitting there with a bowl of down, a big ol’ ladle, and a scale. Maybe that hints that I’ve made a mistake. Perhaps /u/dantimmermade or /u/nunatak16 can shed some light. In any case, I should note these caveats:

• This discrepancy could also be explained by bad estimates of the quilt surface area. If I underestimated the surface area, then the implied down content and overstuff percentage are both biased low, and vice versa. But the only way to simultaneously pull my estimates for both quilts closer to their posted specs is if I underestimated the Zpacks area, and overestimated the EE area. In any case, these estimates came from the posted specs
• “Target loft” might be taken more loosely than I imagine
• I did not compensate for the footbox bottom panels, or the bit and bobs that are found near the head area of the Accomplice. But accounting for either of these would mean taking down content away from the numerator (posted total-down spec) in my estimate of the overstuff error, and drive those numbers down, not up. That might make sene for EE, but it doesn’t help ZPacks

Ok bye now.