Thank you. I am torn between L and XL. My chest is 43" as well. The Flylow hard shell I have is an XL and the fit is nice - no restriction across the chest and under the arms and room for layering.@brian avery . Sorry, don't check in that often. Laid flat my large is just under 25" when laid flat. I have a 43" chest and have plenty of room. Having tried dozens of jackets I can say that the Environ is "medium" roomy. It is halfway between athletic fits like Arc'teryx and looser fits like my Flylow. It is my go-to.