Quailty Piece of Gear
This jacket is top notch. The overall construction and design is excellent. I have yet to test this jacket to its fullest so I will speak mainly to fit.
My specs are as follows: 6'1", 185 with long arms and broad shoulders and 45" chest. Neary all of my gear is XL, as I always have trouble with the shoulders and arm length of my upper body garments if I go with the L.
So with that in mind I originally ordered the Rab in XL, thinking that I would have plenty of room with the jacket to layer underneath. Once I got my gear, it was apparent that the XL was simply too small. The fit in the shoulders even with a light base layer shirt was pretty tight and the arms would ride up. I tried the XL with an Atom LT XL hoody underneath and I felt like a human sardine, unable to move my arms freely. The fit in the waist and stomach area was really good, but I sent it back and got the XXL.
The XXL fit perfectly, a little big with just a light layer on, but with my Atom LT it was nearly perfect. The arms were right where they should be and I had plenty of freedom of movement in the shoulders and upper back. The waist was a bit big and a little boxy looking, but that is a problem I have with nearly all my jackets given my V shape upper body. All in, the fit was exactly what I wanted in the XXL since I plan on using this primarily to layer over the Atom and a few other lighter layers when it is really cold out.
I then put the Atom LT on with the Endurance Neuitrino and topped it off with my Alpha SV shell and it was like a custom fitted winter layering system. I was able to even add the Atom SV to the mix and while the fit was a bit snug, it worked pretty well, not that I will need that many mid layers normally.
My overall take away is that the Rab jackets run 1/2 to a full size small relative to US sizing depending on your overall body type, so make sure you size up if you are at the limit of the stated sizing measurements and/or have broad shoulders/long arms.