How does this thermal & material compare with a 100% silk thermal?Thanks.

I don't have this actual shirt but I swear by Icebreaker in general. This is pretty lightweight for a baselayer (i.e. for colder temp you will want to look for a heavier weight, think more like 260 weight). I find that the merino wool does a better job of regulating my temperature and wicking moisture than silk (plus it doesn't get nearly as smelly), and at this weight it feels like cotton, super thin and stylish to boot. But that's just my opinion. . .