From a person with minimum body fat getting the desired warmth is a challenge. From personal experience I find that a simple Patagonia base layer, and a good insulated Gore-Tex or eVent shell provides more warmth than wearing a number of layers. Basically, more warm air between your skin and the shell will be better than bunch of layers that reduces the air space and trap sweat which enhance the cooling the body.
I have an Arc'teryx Fission SV synthetic insulation (expensive but very durable), and Feathered Friends down (again expensive but very high quality down and no tiny feathers).
I use the Fission SV when:
- Hiking area require a good deal of body motions like the mountaineer route of Whitney.
- There is a chance of scraping against boulders and rock
- Encountering wide range of weather like rain, hail, or snow
I use the Feathered Friend down jacket when:
- Hiking glacier type route, like Shasta
- Weather can rang from like high wind to chilling temperature.
A caution in buying down jacket: From personal experience I have bought a name brand down jacket made in China filled with tiny feathers. It ruin a trip with no warmth. Took it back, and the store mgr felt strange when squeezing the jacket. He poke a tiny hole at the bottom and tiny feathers came out instead of down. When your life may be at risk no more made in China. Before you buy a down jacket try on a Feathered Friends down jacket and really feel it. It is the gold standard. Even if you decide to buy a different brand, you will have a good idea of the difference in quality, and maybe spot one with feathers in the jacket.
Best way to test out an insulated jacket: Go to your neighborhood butcher, and ask to step into his meat freezer (must have door knob inside before you let him close the freezer door!). Within a few minutes you will know if the insulation is any good before you embark on a trip.
