I ordered this lightweight sweater in navy blue size XL, which ended up being too small. Admittedly, this was my own fault as it is clearly described as a slim fit and is something that I did not notice when I ordered. No big deal as Todd Snyder exchange policy is quick and easy and was able to exchange for an XXL, which fits perfect. If you have larger chest, shoulders and arms you definitely will want to size up. Even sizing up, I think this sweater is more ideal for a t-shirt underneath as opposed to a button down but this is merely my opinion.