Sleeping Bags For Below-freezing Temperatures?

[MichaelBSines]

Given equal thermal efficiency, which sleeping-bag fill is best in below-freezing temperatures?

[Kinguq]

I don't understand the question. "Thermal efficiency" is heat input divided by work output, and sleeping bags don't do work. Maybe you mean insulation value? If so, are you are asking about qualities other than keeping the user warm, such as, for example, compressibility and water resistance?

Kinguq.

[Lonelake]

It should be noted if you are using a heated shelter or if your cold camping. The ability to dry out your sleeping bag should be considered when speaking about types of insulation.

LL

[4estTrekker]

For what it's worth, I use the tried-and-true layered system approach for really cold conditions and/or extended trips where keeping my sleep system dry is paramount. I have a down sleeping bag (with hydrophobic down, for what it's worth) that gets topped with a long/wide topquilt made from Climashield. This layered approach moves the condensation point further away from my body and within the synthetic insulation. This outer synthetic layers also takes the brunt of the condensation from my breath. My down bag stays much drier while the synthetic topquilt, although damp each morning, can handle the moisture far better over longer periods of time and dry more quickly.

[Piolet]

I'm afraid the simple answer is to quit fiddling around vainly hoping there's an undiscovered "truth" about what sleeping bag fill/combination works the best in all conditions. Whether or not you despise the admittedly arrogant Jerry Wigatow (a similar situation to conflating Trump's personality with his political positions), the simple answer is that Wiggy's Lamilite bags are the hands down best (that's even true in extreme arctic or antarctic, supposedly "dry" conditions. There's a plethora of information about the accumulation of "ice" in down bags on extended expeditions. that not only renders them less thermally efficient but adds to the weight.