Oh. I thought they were trying to get a handle on what was used historically, not what works better now. Stainless steel works better, too, but they didn't have it 300 years ago.

The fact remains that existing/surviving plaids from the period are thin, tightly woven, and fine-yarned, which match the period descriptions, as well. Sure, a nice thick modern blanket will keep you nice and toasty, but it doesn't replicate what was historically utilized in terms of tartan plaids worn belted. If the latter isn't the desired experience, then no problem. If not, then why not add water-proof, rip-stop nylon to the mix?

Here's another period mention of the "fineness" of men's plaids:
http://medievalscotland.org/clothing...tinwimen.shtml