I bought this as my existing early fall base layer is 5 years old and has just about had it. Assos is just the top end in terms of design and fit. Get the sizing right and everything else takes care of itself. Just brilliant. I'm 6 foot tall and 77kgs and bought the size 1. Have worn this in combination with the intermediate assos jacket right down to 2 degrees and once warmed up felt toasty all ride.
Great undershirt, perfect for cold mornings