Adding down – how much?

Yes, 100 cubic inches per baffle = 1/9th ounce.

How many baffles do you have total?

The fill power of down using U.S. standard over estimates by about 10%. That is, in the standard test, the amount of squish they put from above is less than what you'de experience in your sleeping bag. The European standard is more representative. Thru-hiker is U.S. standard so you could add 10% – 0.12 ounce per baffle.

Is the fabric wide enough so baffles are stuffed already? That is, if you put in more down is there room for the baffles to expand?

Even if the fabric isn't wide enough to allow expansion, it will increase the warmth. When the down is packed in more tightly, it will be warmer for the same thickness of loft.

Just take 1 ounce of down and put it in hood and split the other 2 ounces between the baffles.

Why are you doing this? How much do you want to increase warmth? Do you want to go from 0 degree F to -10 degree F or something?

The bag is supposed to have 10" of loft throughout, so there should be enough room in the baffles. As you said, adding more down will make it warmer even if there's not enough fabric for more loft. It's a -40°F bag and I may see -40°F nights, so I want to make sure the bags has as much insulation as it's supposed to.

There are 15 baffles total, but I think only 2 top baffles need down. There's a third top baffle that feels a little soft. Then there's the hood. So 3-4 baffles that need more down. Ultimately it will be up to the place I send it to. I'm planning on sending it to Down Works.

Ahhhhh… There it is, you said two top baffles

Have you used the sleeping bag? Have you found it to be cold or did you just look at it and notice 2 baffles are a little low?

If it is warm enough why even bother with it?

Anyway, yeah, adding 0.12 ounce to each baffle should raise the loft 1 inch. And if you add more, that's fine too. But then those two baffles will be bigger than the others and you'll want to add down to them to make everything even : )

I haven't used it yet. I'm measuring the loft.

I'm okay with a little extra loft over the shins because I'll have booties and a big parka to add warmth everywhere else. It'll help even things out.

Thanks Jerry.

The fill power of down using U.S. standard over estimates by about 10%. That is, in the standard test, the amount of squish they put from above is less than what you’de experience in your sleeping bag. The European standard is more representative. Thru-hiker is U.S. standard so you could add 10% – 0.12 ounce per baffle.

It’s certainly a good idea for makers from all over the world to overstuff down gear in the range you’re mentioning, no matter how their down was graded.
I would like to point out, though, that my down is not graded using a US-centric testing method. My down is independently tested by IDFL here in the US, but they certify fill power using the internationally adoped IDFB standard 10-B. The International Down and Feather Bureau developed that standard and is headquartered in Austria; more info on the International Down and Feather Bureau can be found at their website http://www.idfb.com

Regards,
Paul Nanian
http://www.thru-hiker.com
(415)462-1745

I didn't mean to criticize your down. You have the highest quality products of any supplier in my experience.

Isn't there a different standard in the U.S. compared to Europe?

And Europe stndard is more conservative?