On the snug side I'd say. My medium is a 'tidy' fit, but I'd not want to be wearing too many layers beneath it. I'm 6'0, about 11st and slim build, maybe around a 40" chest & 32" waist. I could get a base layer and a thin fleece under my Filo, but I reckon it would be a bit restrictive to be wearing much more and still remain active.
ive got the Large size and am 5,9. 43" chest and 34waist. it comes up quite big on me with a microfleece underneath but great for throwing over all my layers and hardshell when standing about.
Ive got last years model so weather the sizes will differ slightly this year im not sure. I did notice quite a price increase this year. not good as its starting to get closer to bigger brand names offering same or similar specs. im sure it will be still a good buy though!