layering advice: arcteryx gamma lt vs arcteryx proton lt as a 2nd mid layer

I do not have any softshell yet and think its past time I get one. I like the sound of the proton lt and gamma lt or bd dawn patrol. I dont have any good outdoors stores near me so havent been able to get my hands on any. So I was wondering what the differences are? (which is warmer, more breathable, more durable, more useful) and which would you prefer for mountaineering in the pacific nw? I would layer over a tnf fleece (similar to pata R1) and a lightweight synthetic baselayer. I would also like to use for ski touring.

I think you need to be more specific when you say, "mountaineering." What exactly are you planning on doing ... technical climbing on rock and/or ice?  Glacier travel to volcanic routes? You've listed the Gamma LT and the Proton LT.  They are two completely different jackets.  

The Gamma LT is a traditional, uninsulated softshell hooded jacket.  It is very durable, stretchy and comfortable with an amazing hood that will accommodate a climbing & ski helmet with ease.  The Gamma LT Hoody will breath pretty well and offer you decent wind/weather protection. Nothing cutting edge here, but sometimes that's exactly what a mission calls for.

The Proton LT Hoody is not a traditional softshell jacket, even though I think I've read somewhere Arc'teryx may refer to it as such.  The Proton LT Hoody has a light, nylon face fabric that is wind and weather resistant.  The Proton LT Hoody is filled with 65 g/m2 of CoreLoft Continuous synthetic insulation.  CoreLoft Continuous is Arc'teryx's entry into the breathable insulation game; competing with Patagonia's FullRange active insulation, Polartec's Alpha insulation and other offerings from PrimaLoft. 

I own the Gamma LT Hoody and the Proton LT Hoody.  I don't wear both combined as the Proton LT Hoody was designed to be worn on its own.  It is wind/weather resistant enough on its own that it doesn't really work very well as a midlayer all the time.  If wind/snow/weather are too much, then a lightweight hardshell, like an Alpha FL, Westcomb Shift LT Hoody, etc. should be worn.  Keep in mind, a lightweight hardshell will weigh a lot less and be a lot more packable than the Gamma LT Hoody.  Even though "LT" is in the title, it's nowhere near as lightweight or packable as a hardshell.

I've found that the Proton LT Hoody does very well on its own and I rarely, if ever, have to couple it with a hardshell, even though I always have my Alpha FL in my pack.  The Proton LT Hoody blocks most wind/precipitation and dries reasonably fast.  If you're looking for a synthetic midlayer with active insulation, I also recommend Patagonia's Nano-Air series.  I have the Nano-Air Light Hoody and the original Nano-Air Jacket.  I find the face fabric the Nano-Air breathes better than the Proton LT Hoody, but isn't as wind/weather resistant, which makes it a better midlayer under a softshell/hardshell when you'll be wearing the shell all day.  Keep in mind though, all these active insulation pieces were really designed to be worn on their own so they can breath as intended.  The Nano-Air series dries faster than the Proton series in my experience.

On that note, your layering system sounds like a bit much, unless you run very cold.  A thin baselayer & fleece layer, coupled with an active insulation piece and a softshell or hardshell is a lot, unless you run super, super cold.  Odds are, you'll overheat three minutes into the approach.  With a little more information on what "mountaineering" really means, I can help recommend a layering system with the aforementioned apparel. 

Thanks for the quick advice Alpine Ice

Mountaineering for me is glacier travel on volcanic routes and planning on getting into some more technical routes with mixed climbing. I'd like to take some combination of this system to bigger peaks some day. I run pretty warm so would a system without a fleece layer (base layer, active insulation, shell) be more effective for the dc route mt rainier for example? Planning on giving it a go mid summer. I have the alpha AR now, are you saying it could go well with the nano-air series or atom lt? 

I've never been up on Rainier, but slogging up hill for a few days makes one think that you'll work up a sweat and stay pretty warm most of the day.  I know Liberty Ridge is one of the more technical routes on the mountain, which would warrant little more thought and practice with your apparel system due to belays, etc. 

That being said, I don't want to give you advice on a layering system of for a mountain I've never set foot on.  there's probably a hundreds of people on MP that have climbed Rainier and can better guide you on what they wore.

This is my advice and take it for what it's worth - I think people mistakenly think the base of their climbing apparel is their technical hardshell.  When's the last time anyone wore a hardshell and though to themselves, "Man, this thing is so comfortable!"  The truth is, they're waterproof, but not breathable.  Unless you're actually technically climbing some WI 4 or higher at elevation, a hardshell is pretty worthless as most people over heat within ten minutes of slogging up hill.  An ultra lightweight hardshell is a great piece of gear to have if it's balls cold and windy or climbing waterfall ice with nasty, drippy conditions.

I think, with the advent of active insulation, that's where your concentration should be and where the foundation of your layering system should start.  For me, a super thin baselayer (Cap 1), a Nano-Air Light Hoody, which uses 40 g/m2 of FullRange insulation and a Proton LT Hoody with 65 g/m2 CoreLoft Continuous has gotten me pretty far in some very, very cold weather.  Add a hardshell if weather/wind warrant it and a thick belay jacket to top it all off.

I live/climb in the northeast where it hasn't been much above 0ºF the past week.  Winters can be very, very cold with a lot of lake-effect snow.  I've found that active insulation does work pretty well as described.  The light and airy face fabrics, coupled with the porous insulation allows decent venting while I'm climbing.  The face fabrics dry really fast, even in severe cold, which allows me to wear them without a hardshell ninety-one percent of the time.

Your needs may very, but it gives you a starting point.  If you're looking for a really good midlayer and you run on the warmer side, I'd choose the Nano-Air Light Hoody over the Atom LT Hoody.  For a little more warmth, check out the Nano-Air Hoody.

thanks mate 

I think I'll start looking for the nano air. I'm looking for something to wear as an outer layer most of the time until the conditions worsen so I would want it to be more protective than the nano air light. Is it true the newer version has a 30D nylon shell? I'm thinking that might be more what I'm looking for as it should show less signs of wear and may last a bit longer. How's my thinking process here?

For your outer-most layer, I'd go with (and I did) the Proton LT Hoody.  It's a bit more weather/wind resistant and adds in the durability, over the Nano-Air series, you're seeking.  I'm not sure about the newest Nano-Air face fabric.  My Nano-Air Light Hoody & Nano-Air Jacket are last year's models.