Temperature rating per inch of loft?

[MotoHanger]

Here is another thread about CLO ratings and some references to Down and what the theorized CLO rating would be, which could then be used to roughly calculate temp rating in pristine conditions depending on the individual of course.

https://www.hammockforums.net/forum/...ead.php?t=2181

[Flash Grundelore]

Anyone have any info on loft/temp ratings for older down fills?
I have two great old bags [30 and 40 yrs old/baffled]. I used one a couple of years ago right after I started hanging, woke up with it down to 20° and, as I remember, I was perfectly cozy.
Both were high-end bags when new [Gerry and Bauer], but neither has a rating tag or indication of the fill-power#s. The thicker one is close to 4" of single-side loft hung and fluffed.
Any guesses as to temperature ratings?

So... is there any effective difference in the insulative power of older, lower rated downs, or is it just the weight-per-gm benefit?

The reason I am asking is that I never really need a TQ to take me down below 20°, but I thought I might do a mod on one of these by taking the hood and zippz off just to have a "go-low" option if I get crazy.

[MAD777]

This is the formula I use when making gear. It follows the conserva Mountaineering company ratings closely. It's also fairly easy to remember.

Start with 70°F and subtract 20°F for very Inch of loft.

Therefore, the rating for 2" of loft would be 70 - 2*20 = 30°F

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