Fleece is considered heavy for "true" UL use and it is bulky when packed. As a PNW resident, I like the stuff for cold rainy weather. Standing around the fire with a fleece on a damp evening is camping to me :)
There is much debate on down vs. synthetic fill. I recommend synthetic if you hike on the West side of the Cascades. Many will disagree.
An example of an UL layering system:
Starters:
Silkweight base layer top (some prefer Merino wool; I like polyester)
Briefs
Pants/shorts (I prefer convertibles. Light soft shells are nice in cool/wet weather)
Socks (I like Merino wool)
Windshirt.
A windshirt is an UL standard. Go there before button-down long sleeve shirts. It will keep the wind from stealing the heat from your body and should repel light rain. It should be breathable. They can be good insect protection as well. I recommend a lighter color, so you can wear one in direct sun without baking.
Insulation.
Thin insulated jackets like the Month Bell Thermawrap, Patagonia Nano Puff or down equivalents are popular. I like one with more loft (and more weight), like the Mountain Hardwear Compressor or Patagonia Micro Puff, finding that the lighter insulators don't provide enough warmth. Vests work too. I like the Patagonia Micro Puff vest a lot. A down vest could work too– as long as you keep it nice and dry.
I like a mid-layer for some weather, with Power Stretch being my favorite. Patagonia makes some thicker Capilene tops— choose to your liking for metabolism/weight/cost. I don't think this is an "orthodox" ultralight choice, but it works or me, especially under a shell in wet weather. I think a Power Stretch vest rocks with a shell.
Rain shells
Typically 2.5 layer jackets and pants like the Marmot Precip (get one with good ventilation). Many use Frogg Toggs/Driducks. Some use a poncho, which doubles as a minimalist shelter. Event garments are on the increase; nice but $$$$. You will find a number of super thin shells like the Marmot Super Mica. Some use rain wrap/skirts or chaps for rain bottoms.
Big puffy jackets. Typically for rest and camp use in colder weather or for those who just need more insulation. Western Mountaineering down jackets are probably the most popular here. Too warm for most of the hiking I do.
Hats and gloves. Fleece beanies, big floppy sun hats, light fleece gloves, mitten-style shells with liners, etc. (I like shelled gloves for wet weather).
I usually head out from the trailhead with the basics plus a windshirt, ventilating or changing as needed. If it gets wet, I'll put the windshirt away and go with a shell. If I'm not going up a steep slope and I'm cold, that is where the mid-layer comes in and a vest is usually plenty.
In camp is where the insulation comes in play– enough to keep me warm while sitting around, eating or resting. That insulation can be worn for sleep to extend the range of my sleeping bag too. Those Power Stretch mid-layers I like so much really come into play for sleep.
I find that hats and gloves really help with the perception of cold. Often your body isn't chilled, but your hands are feeling it, making you think it is colder. Hats are protection from sun, rain and cold.
I like shelled gloves for rain– just like rain shells for my hands. My current gloves have a breathable shell and a light fleecy lining. I use trekking poles, so my hands are out in the rain.
I like a Tilley brimmed hat most of the time. The Peruvian style fleece caps with ear flaps are my favorite for cold weather and sleep. They work well under a hood too. I recently added a Gore-Tex baseball cap and it rocks under a hood— the bill keeps the hood out of my eyes.
Some like gaiters. Long ones are good in snow and wet brush. Short stretchy ones will keep the rocks out of your shoes, add water repellency and keep your cuffs out of the mud.
