Most people say that high quallity down is warmer for its weight vs the best synthetics. Is this true even for the warmest and thickest down clothing too?
For example, many people say that the Rock&ice parka from Feathered friends is one of the warmest downjackets in the world. It has 21oz of 850fp down and i understand that it has a Clo value of ~12.
Thats a warm jacket no doubt about that.
But if you take 12/21 you see that its only .57 clo/oz of down filling, that dosnt seem like a good warmth/weight ratio to me.

If you were to use 21 oz of Primaloft 1 in a jacket you wold have ~.9 clo/oz *21 = 18.9 Clo value. So Primaloft 1 seems to be about 50% warmer for the same weight of insulation used compared to down.
If synthetics are warmer than down filling in higher densities then why do manufacturers use down in their warmest garments?

Theoretical insulation is very different than real, tested CLO.

I think your calculations may be based on faulty data... I seem to remember seeing clo / oz for down being in the 2-3 range depending on the fill power (550-900). So the clo for the jacket with 21 oz of down is probably at least 42.

I may be wrong on this but i think fully lofted down is more efficiant than synthetics. fylly lofted 800fp down has a density of 1.62oz/yd2/in3. at that density you would have to make one thick jacket to fit 21oz of fully lofted down. You cant make a down jacket with 8" loft. The thickest jackets is ~4" loft. 21oz of down in a jacket with 4" loft means that the jacket is overfilled. overfilling a jacket makes it warmer but every oz you add is less efficiant than the last so the warmth/weight ratio goes down.

And the 12 clo value for the down jacket is Richard Nilsey's number so i think its correct

Hi Robin,

Maybe I am wrong but its two different insulation measurements,

Down is measured in overall weight and synthetic in grams (or ounces) per square meters (or yards) so say 100gm2 Primaloft One has 100g weight of material per square meter.

Cheers,

Stephen

Edited by stephenm on 02/08/2013 12:23:53 MST.

A hooded jacket takes 2 to 3 square yards of fabric, so 21 oz of synthetic is more like (21 oz / 3 sq yards)*0.9= 6.3 clo (or 9.45 clo if only 2 square yards are used).
It's worse than that because Richard Nisley's measurements show synthetic insulation performing much worse than it theoretically should; from memory, the synthetics give only half the insulation that they should. So, your 19 clo jacket might really be a 3 to 5 clo jacket and you'll freeze.

Also, just like sleeping bags, the advantage for down becomes greater the colder the temperature rating.

Thank you Walter! That makes sense!