Firstly, thanks to all the previous reviewers this item runs very small. I took the advice of others and bought 2XL and it fits perfectly, a little long but will tuck in nicely. I'm 5ft 10in, 37-38 chest 165 lbs. Usually medium rapha jersey, large castelli jersey and large pro castelli base layer. But this base layer just about fits like the large pro issue castelli which is for me a size up already. Other than sizing I can tell merely by the design that this base layer is what you want for a hot day above 85 degrees F. I wear the normal and sleeveless castelli pro base layer in 80- 85 degree weather but above that I feel hot. The pro castellibbase layer is thinner than the core 3 but the pro does not have actual openings between the mesh just varied thickness and is very thin. This is the next level with large mesh openings. Hope this helps.
fits very tight and very uncomfortable was not a good buy for me
The core mesh creates an isolating layer that promotes warmth in the cold and allows heatmoisture to escape when the morning ride heats up. It fits snuggly like all Castelli products. Only drawback is the tag placement on the side, needs to be removed.