99.8%
Aerogel is almost entirely air. Its hollow, nano-scale molecular structure makes it one of the most highly insulating materials in existence.
Down feathers may be the animal kingdom's best insulator, but those feathers need to come from somewhere. There is the Responsible Down Standard, which many big brands like The North Face, Marmot, and Mountain Hardware adhere to, and it states that feathers should not be plucked from live animals, but it would be great to have an alternative that didn't leave any room for ambiguity.
Oros is using aerogel fabric in a bunch of outerwear, from lightweight vests to full parkas like the Orion. Its website claims "max-warmth, zero-bulk," clearly calling out down jackets.
Yes, extremely. Oros claims that the Orion is good down to -40°F, but I wasn't personally able to test that. The jacket was very warm during my testing at around 50 degrees on these chilly fall nights, and if we have the chance to test these jackets again during winter's most punishing months we absolutely will. But to be clear, at 50 degrees I was uncomfortably toasty.
Down jackets are just too bulky for some people, and as a matter of style, I get that. In the outdoor space, down jackets are also valued for their light weight and the ability to pack down really small. But if you're not going hiking, does that really matter?
If you just can't take the bulk of a down jacket, the Orion parka could be for you. It's heavy and a little expensive, but it's also highly water resistant and nicely made.
We won't be able to fully test the Orion until the temperature dips below freezing, but something like Oros' Atmos zip-up hoodie would be more ideal for fall weather. Until then, stay warm out there.