I have 3 different winter cycling tights, all polyester or polypro but of increasingly thicker/heavier/warmer construction. The warmest of these were made by Performance about a dozen years ago; these are unpadded, so I wear them over cycling shorts, and they're good down to about 20°F.
I also have a pair of...er, well, I guess they're "tights" though they're not particularly tight, they're actually kinda baggy like pleated trousers...that I wear for commuting, they're got a fuzzy/fleecey lining and they're also good down to about 20°F. (But not particularly aero.)
I have often surmised that I could wear the baggy pleated fuzzy/fleecey tights over the Performance tights and be good to well into the single digits. But since I don't have shoes or gloves that I trust at those temps I have yet to try it.