I was surprised at how small a package this arrived in!  It's not a bulky vest by any means.  It feels very light and looks like it would be comfortable to wear even on warm days.  And so many pockets!  All of them zippered which is fantastic.  I'm not sure how it will hold up under use being on the thin side, but on the other hand it's not expensive so if it lasts a few years that's a deal.  I am 5'7", 42" chest, 33" waist, and I got the Medium. It is plenty large for me, but it wasn't so large that I felt I should have got the next size smaller.