I've had a traditional red wool union suit for decades - long johns. I don't recall the name - they're still in the bottom of the closet in the winter wear bag, since it's not quite cold enough yet here in Texas. But they came from LL Bean, Lands' End or some place like that. Good quality. The only noticeable sign of age is a few tiny holes from critters nibbling. Over the decades I've worn them for winter commuting by motorcycle, while doing yard work, etc. Very soft and comfortable, even when wet from rain or snow. Perspiration wicks away properly, so they're comfortable even when working hard.

I'll dig 'em out soon since we've had a snap of chilly rainy weather and I'd still like to ride my bike.

I also have two or three sets of two-piece synthetic winter underwear, poly-something or other. Comfortable and warm, but I still prefer the traditional wool. Both the wool and poly-whatever have been warmer than silk. I like silk shirts for sweaty humid summer wear, but it's not as good for winter wear.