My friend Liz asked me about my layering system after a recent trip. what you are about to read is from an email I sent her. There may be mistakes or omissions because of the nature of the text. I simply copied and pasted the email here on this site. I will edit and update as I find time, mistakes, omissions, etc. Thanks.
If you want to know how I stayed warm then I guess you're asking me about my layering system. I'll tell you my system but remember it is just what works for me, every person and situation is different. This will help guide you to figure out what layering system you want/need and what elements you'll need to put together a system that will keep you warm and dry. I'll tell you the brand names of what I use, but I'm not saying this is the best gear out there just because I use it. I use the brands I list here because they are what works for me, that is what is important; that you find gear that suits you and your needs as a backpacker. There are many good manufacturers out there making gear that is as good or superior to what I might use. So just get the basic knowledge here and then find the gear that works best for you.
BASE LAYER = Your bottom layer, the one that touches your skin should be made from a fiber that wicks moisture. These fibers include synthetics and wool. Base layers come in different grades, meaning you can buy a base layers in a range of weights from light to heavy depending on how cold you expect to be or how sensitive you are to the cold. Remember you'll be exerting energy as you hike, and you may want to factor that in and maybe buy a lighter weight than you normally would need so you don't overheat. For example, I use Patagonia Capilene for my base layer and my pants are mid-weight but my shirt is heavy-weight (because I usually hike without a mid layer I use a heavier shirt). You should always carry an extra base layer set of shirt and pants in case you get wet. Like I said I use Patagonia but other good base layer brands are: Ice Breakers / Hot Chilis / Mountain Hardwear / REI
MID LAYER = This layer should consist of either a fleece jacket or a pullover. If you want to break with tradition and try out a mid layer that could be considered both a mid layer and a shell, then a soft shell jacket would actually make an excellent mid layer, rather than its role as an all but extreme weather shell(yes, that is confusing). I will talk about the soft shell a little later, right now lets talk about fleece. I used to use a fleece jacket for a mid layer, but not any longer. I feel they are too heavy and bulky to carry around since I usually don't wear the mid layer anyway unless I'm stopped for a long break and start to cool down, or I'm doing things around camp and beginning to cool down after the hike. Maybe if the temperature really drops I'll put on my mid layer, but usually when I hike I wear just a base layer and a hard shell. You can wear your mid layer with the base layer if you want to as you hike, and pack away your hard shell. If there is no wind, and the temperature is not real cold, and there is no rain, or snow, or ice that can fall onto you from trees, etc., then you can wear the mid layer and base layer togeather with out the hard shell. I told you I don't like fleece jackets as they are too heavy/bulky. But a fleece can be a very good mid layer, especially if it has incorporated into the jacket polartec windbloc (I know The North Face and Mountain Hardwear jackets have polartec), or if the jacket is a heavyweight fleece - which can be quite warm. Now lets talk about soft shell jackets. Try using a soft shell jacket as a mid layer instead of as an exterior storm shell. I’ll explain. A soft shell jacket isn’t really an extreme water/snow proof garment, they are only resistant to these elements due to the fabric type and a DWR treatment applied to the fabric. Eventually, in extreme weather the soft shell's permeable fabric and DWR coating willeventually break down and will no longer keep you dry. So an alternative is to wear your soft shell over your base layer in all but the most extreme weather at which time you can put on your hard shell jacket. Now lets move on to what I use as a mid layer. I use a synthetic insulated pullover as a mid layer, it's called the Nanopuff pullover and is made by Patagonia. It's light weight and packs down small and if I use it between my base layer and hard shell I begin to sweat, so I only use it during stops as my body cools down or when I reach camp and begin to cool down. There are many different synthetic insulated pullovers out there, meaning differences in the synthetic fibers that make up the pullover's insulation qualities, and differences in weight and design. A synthetic pullover is like having a down jacket with out the puffiness. You can also find pullovers made with fleece or wool, or wool/synthetic mixtures. If you don't want to carry a heavy fleece jacket but still prefer the insulating qualities of fleece or wool over a synthetic you can find a pullover out there made from just about every fabric imaginable. I just prefer synthetics because they are light, pack small, keep you warm when wet, and will also dry quickly.
I consider the pants you wear as part of the mid layer, because if it is raining or snowing you will be putting on the hard shell water/snow proof pants you brought along over your soft shells. I use a pair of Kaikkialla soft shell pants that I bought in Europe because they were actually pretty cheap compared to what you pay here in the US. Soft shell pants do a good job of repelling snow and will keep you dry and insulated against the wind. But because they are not totally water proof just like with a soft shell jacket you need another layer. I can wear the Kaikkialla pants in all but the most extreme conditions, then when I need to I’ll throw on my Wild Things Superlight Alpinist eVent hard shell pants on over them. For this protective pant layer you can also use ski pants, or even insulated pants made with synthetics if its going to be real cold where your going. I avoid down in mid layer pants and tops because if the down gets wet you’re in trouble. If a synthetic gets wet it will still keep you warm and will dry faster.
HARD SHELL = The exterior layer, a jacket that can withstand wind, rain, snow, and abrasions from branches, rocks, etc. I use the Cloudveil Koven Plus jacket and a pair of Wild Things Superlight Alpinist pants for my hard shell top and bottoms. The Koven and the Alpinist pants are made with eVent fabric, which I like more than Gore-tex because it is warmer and blocks wind better and is only one layer of fabric while Gore-tex is several layers of fabric. There are other water proof fabrics out there so look around and use what’s best for you. The main thing is you want your hard shell to keep the rest of you dry. I've worn my eVent jacket and pants in six hours straight of rain and stayed dry. On my trip this past Saturday, when I had to crawl under trees downed by snow the eVent fabric seemed to shed the ice that was falling on my head and back. The wind was blowing hard and both shells did a good job of blocking it, which goes a long way towards maintaining a comfort level. Inspite of being inside a storm around an elevation of five thousand feet, I never got wet or got ice on my skin while wearing my hard shell jacket and pants last Saturday. That is what a hard shell should do, keep you dry and keep wind off of you.
DOWN JACKET = I always carry a down jacket in my pack when I expect temperatures below freezing. I don't wear it except when I'm in camp and after I have cooled down. This is generally at night after the sun goes down and in the morning when I first get up. A down jacket that is packable like The Rab Ascent jacket I use is perfect because it will pack up small inside your backpack until you need to take it out in camp at night. Nothing will keep you as warm as down and it is also good to have because you may need to dry out your other layers (or get out of them anyway because they might be wet). Usually I can wear my down jacket with just the baselayer at night and be plenty warm. And if temps really get bad like in single digits or sub zero you can always throw on the down jacket underneath your hard shell while hiking. Or if your sleeping bag isn't cutting it in the cold you can throw the down jacket over yourself as an extra layer at night.
In a nut shell on Saturday I hiked with a Patagonia Capilene zip top as a base layer and then my Cloudveil jacket over that. I had on Capilene bottoms for a baselayer, and over that I wore my Kaikkialla soft shell pants, and over them my Wild Things Alpinist pants hard shell to stay dry. Of course I wore insulating and wicking baselayer socks with Mountaineering socks (Smart Wool brand), and over those leather boots. I had a pair of Marmot gloves made with Gore windblocker and some wicking glove inserts to go under them. I also had a Balaclava made by Hot Chilis and another winter beenie made by Turtle Fur that has windstopper technology.