A fleece is a fleece is a fleece. Well at least it was up until a couple of years ago when many of the higher end companies started piecing together aspects of their fleeces, downies and sythetic filled jackets into mid layer hybrids. I guess what they were noticing is that many people were using their lighter down and sythetic filled jackets as mid layers for colder weather so they jumped on this band wagon and decided to do it right. By "right" I mean that a mid layer has two jobs - one is to keep you warm but the other is to keep transferring sweat outwards. Although they do breath, often down and synthetic puffies don't do this as well as fleeces. So outdoor companies started designing jackets that promised to be a mid layer but better.
Mapping the warmth is the idea of conertrating insulation to certain parts of the body that benifit most from it, and having less insulation at other points either to make the garment lighter, less bulky or more breathable. We've started to see more of this in recent years and not just in the outdoor industry but also places like the surf industy with wetsuites. High-end, cold water wetsuites having concertrated warmth (even electronic) around the kidneys has been shown to be quite effective to increase overall body temperature without having to have a super thick wetsuite all over.
What garments like the Acetylene jacket are trying to do is concertrate wartmth to the front side of the core, the kidneys and the shoulders via Primaloft Silver but reduce insulation on the arms and the back using the RadientLT fleece. The idea of keeping the core, kidneys and shoulders warm is pretty obvious; keeping them happy is the first big step to keeping your extremities functioning normal in cold conditions because the core won't try to steal back all the blood to protect itself. The problem with having a highly insulated mid layer though is that when you start moving you can quickly over heat. Which is not only anoying, but also detrimental to permormance. Having the Radient LT fleece on the arms makes movement (climbing or skiing) a whole lot easier, and having the back in the lightweight fleece also means that excess heat and sweat can easily get out.
What this jacket gives you is a mid layer that works over a wide range of temperatures when you are doing a high aerobic activity, and breathes incredibly well. The front is basically windproof which is great for skiing (because hopefully you are moving forward at a reasonable pace) but also for mountaineering (because usually your pack shields your back anyway).
I've used this jacket over a number of seasons now and love it to bits. If you're being active in cold temps this jacket just works. Your core is always protected and warm yet even when you start sweating you don't feel like you need to take it off. You have great freedom of movement with lighter, stretchy fleece on the armes and the pockets are great for keeping liner gloves and batteries warm during the day. I've givin mine a good bashing and it has stood up to a lot of abuse.
The limitations of a jacket like this is when you are sitting around in the cold doing nothing. If you're looking for a jacket to keep you warm in sub zero while you sit and take photos - don't buy this, it only makes sense when you're moving. If you stop for too long while wearing the Acetlylene your back will get chilly. This is easily overcome by putting on your belay puffy anyway but don't think it is the one jacket to rule them all. It does however rule the technical fleeces.
The fit is trim arount the core which makes it good for layering. The arms were a tiny bit baggy for my liking. I expected tight arms but this fits more like a traditional fleece on the arms. Maybe I need bigger biceps. The big gauge zippers are easy to use with gloves and take a lot of abuse. Cleaning is fine, just treat as a normal fleece.
Matt doesn't like it too warm or too cold. He likes it just right