I also posted this on reddit in u/ultralight. I could use folks expertise here on how to rationalize the 1000fp in the Ghost Whisperer UL compared to a more traditional 105g 850/900fp jacket.
Item: Down Jacket
Baseweight: 10lb
Location/s of use: Cascades & Olympics
Season/s of use: three-season
Expected temperatures: 20-50F Ideal weight of the item: 7-11oz
Additional Information:
Trying to decide between Arcteryx Cerium LT, Mountain Hardware Ghost Whisperer UL, and Feathered Friends EOS.
It seems like the Cerium LT is the best deal (on sale). FF Eos should be a little warmer than the Cerium due to the 900fp down over the 850 in the Cerium yet same amount of down (105g).
I’m not sure how to factor in the GW UL. With basic math, it seems the UL version would have the same amount of warmth as the regular GW despite the lower weight. 1000fp is 20% more efficient than 800fp. The regular GW has 80g of 800fp [1]. Therefore, 65g of 1000fp is about equal to 80g of 800 fp. Is anyone able to verify my calculations here? Is it as simple as “Do I need more or less warmth?” Did I miss anything? The GW UL also uses 5D fabric. Is that too whispy for practical use as “stop” insulation?
Jacket – Overall Weight – Down Weight + Fill Power – Price (USD)
Arcteryx Cerium LT – 10.8 oz – 105g 850 FP – $264 – on sale
Mountain Hardware Ghost Whisperer UL – 6.67 Oz – 65g[2] 1000fp – $281 on sale
Feathered Friends EOS – 10.6 oz – 105g 900+FP – $340
[1] https://andrewskurka.com/backpacking-clothing-stop-insulated-jacket-pants/
[2] The amount of down by weight is not listed officially for the GW UL, but I confirmed the weight by calling mountain hardware. It’s 60g for size small and 65 for size medium.

