To test these I went for a 15 minute walk, wearing them under a pair of jeans. It was 19 degrees (F) and the sun had been down for a couple of hours, so it was pretty chilly but not frigid. Cold enough to numb your face a little. I stayed totally comfortable throughout (aside from the numb face.) I even sat on a metal bench at the bus stop for a few minutes, and remained pretty well insulated.

The fit on them seems true to size. I ordered medium. I'm 5'10", about 145 pounds, with a 32" waist. Under slim straight jeans I notice the extra bulk a little, but they're still quite comfortable. They hang a little low in the crotch so they bunch up a little bit around that area.