Great jersey. Nice design, pretty much replaces a wind vest for cool days. It runs a little warmer than a typical thermal LS jersey, and fits a little looser than their other LS jerseys, so you can layer underneath it and use it as a close-fitting jacket if it isn't too cold. W/base layer, good down to the low 40's: low to mid 50's without a baselayer. Runs true to Castelli sizing; if the chart says you are a medium, then you are a medium. Except with one pair of bib shorts, I have always found their size charts to be extremely accurate, so I would not recommend to "size up" even though it seems that is what others recommend. Maybe their tape measures are broken? My specs: 30 inch waist, 38.5 inch chest, 5 foot 9: this fits me perfectly in medium, just like the chart said it would. The large is much too big, unless you want to wear a down sweater underneath. Seems to be built well, and fit is tailored to a cycling position
Downsides: lacking windproof material all the way out the sleeves. If you are wearing a SS baselayer on a crisp day, your arms will be cold. Wish they had extended the windstopper material out to the cuffs.