I wear this over a merino baselayer and under a thermal jersey for rides in the low 40's, upper 30's F. Very warm and fits snug in between layers. Very impressed with how warm this is without being bulky at all.
My first reaction was how is this going to be warm....OMgosh... What a mistake. This is a warm layer. Not a windbreaker, which is what makes it great for cool rides and very breathable to not even need to take it off when climbing hills. Pearl Izumi... You nailed it on this one.