Well, Josh, I have to be honest. I don聮t even begin to agree with your premise. True, there is the historical model of the 聯bedroll,” which of course helped win the West聟or helped rob it from the folks who were already there. But I can聮t even imagine trying to use a blanket for anything halfway serious.
Aircore BlanketLet聮s look at an example. I聮m going camping where I expect to see low temperatures of around 35 degrees. Chilly, but not real cold. I could, per your theory, pack along something like a Aircore Blanket ($50), which is made with Polartec 200 and is a nice warm blanket. Now, I happen to HAVE one of these and it tips the scales at about 15 ounces. And I would need two of them聴at least. So we聮re close to two pounds.
Meanwhile, my U.L. SS Down Hugger #3, rated to 30 degrees, weighs one pound and seven ounces聴seven ounces less than the two blankets. Plus it聮s warmer because the Polartec pieces aren聮t that windproof. AND…the sleeping bag is much more resistant to drafts coming up from around the floor. One could shave some weight off the blankets by trimming them down to a more oval shape, but then you lose the ability to tuck the edges under yourself. OK, the bag costs $260, but for its vastly greater performance I don聮t think that聮s bad.
If someone has numbers that make more sense than this, send them on. Otherwise, I聮m sticking with a sleeping bag.