I don't think LL Bean is ultra-liberal, not sure about Lands End but I don't support REI as they tend to align with anti-access groups such as the Sierra Club et al and don't generally support true public lands access for all (I'm not a big proponent of wilderness or limited access to public lands, within reason), hunting, motorized rec or other pursuits I enjoy.I’ve gotten LLBean, Lands End, and REI in the past and they’ve all done the job…
Maybe that reinforces why many sleeping bag liners are silk. Interesting, and I'm getting ready to find out in 3 days in WyI used to pal around with a Brit in Alaska... We hunted, climbed peaks, and skied everywhere. I thought I was pretty tough in those days, but when we had to sit for a few hours... he could always outlast me. He was kind enough to share his secret: silk base layers. Ounce for ounce, some of the most warmth you can get. Really surprised me. Especially in wind.
Merino wool wasn't a thing in those days, so I usually ran polypro/capilene on top of silk. Nowadays I run merino on top of silk, then whatever is outside of base.
Hope that helps!