Which UQ on top, synthetic or down?

[dakotaross]

With down next to your body, its going to be more efficient in trapping heat and, therefore, keeping you warm. That is both physics and physiology as down tends to have more of the cozy factor that you can feel as the volume of air within the down heats up. That cozy factor can have a physiological effect that affects the physics. Synthetics can have the same effect, but typically not as pronounced as down would be. Down can be compressed some and still insulate near its capacity, but only just a little bit so that you do have to be careful there.

That said, what if you're just being overly cautious in terms of your need for insulation? What if you've slept cold at 30 with your 20 UQ and want to simply supplement. Just want to be warm, right? A little too warm and you amp up the perspiration factor. In that case, the synthetic next to your body makes more sense. Also, what if you're really pushing it and you need all the loft you can get. Then Paul's right that you would worry less about compressing the synthetic with the down on the outside. Caveat there is that down is more wispy and synthetic typically has more structure to it, and therefore, synthetic will be less compromised when the wind blows. UQP helps but doesn't prevent warm air from being compressed out of the quilt by wind.

In short, down feels more cozy and is a more efficient insulator when close to your body (assuming limited clothing). Synthetic is a better barrier to the outside elements. IMO, you are not getting 1+1=2 by using two quilts. Rather, you are insulating the primary quilt so that its much more efficient at insulating at its rating and a little beyond. That's in general as you are getting insulating value from the outside quilt, but I believe its incorrect from a practical standpoint to consider the combo as 1+1 in terms of temp rating. This is mostly due to the imperfect way that the two inevitably come together. If you could have them aligned perfectly with no compression, then yeah, at least close to 2.

Sorry for the long response, count me in with the down group, with a healthy dose of "it depends".

[OneClick]

I was told by the people at Enlightened Equipment to use the down closest to you and the synthetic as the outer layer. This is from a condensation point of view. If water vapor from your body ends up turning into liquid, it will most likely happen in the outer layer of the quilt stack. Since the synthetic material stays warm even when wet, best to have that one risk getting wet instead of the down.

No question, down next to the body so that any condensation collects in the synthetic.

BOOM! Science. I agree. If the synthetic is compressing the down too much, you have the worlds heaviest synthetic quilt and that should be enough on it's own anyway!