I have seen an ad in the Camping and Caravan Club magazine for Zerorub base layers. The claim is that as well as offering  wicking and  insulation the rubbing of the inner layers of fibres actually generates heat. (And they seem to offer something for the summer that actually cools you down). As my wife always suffers from being too cold in winter and too warm in summer these look  a likely Christmas present - thermal underwear preferred to lace these days! But does anyone have any experience of whether these do perform as they claim?