Stretchy material, very comfortable. Just remember that Castelly usually runs 1 or 2 sizes smaller. You can try using their recommended size tool on their website, have in mind that their size guide mentions the maximum measure, not an average. For example, I got an XL, according to their website, it would be 108cm for the chest and 94cm for the waist; I'm 107/92 and the jersey fits tailored, not "relaxed fit" as the website suggests nor baggy/flappy. Other than that, I'm more than please with all my Castelli ride wear.
This jersey is a little more expensive than some others but it's worth the extra money. Lightweight and flexible but loaded with features like the zip pocket and elastic waist. Very nice jersey.