This isn't necessarily true.
You can get alpha shirts that way less than that. I'm 5'9 150 athletic build and rolled my own 60gsm alpha direct fleece I ordered off eBay and it weighs 2.5 oz last I checked.
You can then pair this with a Copperfield wind shirt and you have an extremely versatile combo for activities or stationary warmth.
I used to use a Houdini for wind / rain but never liked it's pack size (bigger than coke can). The Copperfield packs down WAY smaller and alpha direct is insanely compressible and DOESNT lose loft / effectiveness like packed down will
Everyone always forgets down isn't suited for long term travel due to this and the loft being killed which is how it's warmth works.
A conversation
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I was using 90gsm in the R value comparison.
I tried a wind shirt in the past and it wasn't waterproof when I needed it to be, so I'll wear the lightest rain coat.
The montbell loses its loft when packed but within 15-30 minute of wearing is back to normal (and I suspect it's warmer than the alpha even when half-compressed). I usually only pack it tightly when I'm nowhere near cold weather anyway. My bag is empty enough that if I take it off to go inside somewhere I'll just stuff it in.