Keith Kwiatek wrote an answer about Pearl Izumi Elite Thermal Barrier Jacket - Men's on November 16, 2010
I just took 3, 40 mile rides this past week wearing the Pearl Isumi Elite Thermal Barrier Jacket. Temperatures ranged from 37 to 61F. It performed very nicely. The front of the jacket has a fairly wind proof material with a fleece like backing. The back is fleece backed spandex like material. The sides and backs of the arms are also fleece backed spandex. It breaths very nice, yet does a decent job keeping the cold wind from chilling your core. With the right base layer, you might be able to go lower than 37 degrees, but this jacket might be a bit too ventilated for 20 degree weather.