Heavier layer – or more layers for increased cold

I never take more than base layer, insulated layer, jacket, quilt

If it's 20 F, I'll take a thicker insulated layer

Fleece or fabric layers, provide very little warmth for the weight. Down is much better. Synthetic isn't as good as down but offers some other advantages.

If you have two insulated layers, then you have an extra inside and outside lining which weighs something but contributes little warmth. But, if that was a 1 square yard vest with 0.7 oz/yd2 fabric, that would be just and extra 1.4 ounce, plus any zippers or whatever, so maybe insignificant. If you had an extra 2 square yard jacket with 2 oz/yd2 fabric, that would be an extra 8 ounces plus zippers and things.

If you have a fleece layer, that's maybe 12 ounces. Add 1 ounce more down and you'de be just as warm.

I subscribe to the "action suit" philosophy in which Layers fall into three categories:

Insulation/moister management layers to be warn while active.
Shell Layers
Booster Insulation layers that are worn at stops or when it gets really really cold and don't need to handle moisture well.

I generally prefer to use wool/gridy fleece for the first layer and avoid too much layering to allow moisture to move out more easily and reduce fiddle factor (ie i might wear r1 bottoms and soft shell pants, a merino t shirt and add r1 hoody and softshell top or windshirt as needed. I find the comfort range of griddy fleece greater then that of non griddy fleece so it is better to bring one layer of that then two of thin merino or polypro.

For booster layers …which may be more what you need since you are sleeping in them and not wearing them during the day? I prefer poofy layers. I like to keep it simple with fewer layer to make it easy to take them on and off when I stop moving but one synthetic layer and one down layer is nice as it lets you deal with some moisture. Say a nano puff and a light down coat.

My system is primarily designed for ski touring which may involve more more moisture and a larger temperature swing then backpacking.

Fleece and knit synthetics are great exercise clothes at 40-50-60F. But as Jerry points out, their warmth/weight isn't great. Lousy, in fact. At those temps, thin puffy layers are lighter but down is at risk of getting wet from rain or sweat.

At lower temps, you have to go with puffy clothes. And down gets more viable (compared to synthetic filling) when you can trust the entire trip is below freezing.

As you get below about 10F/-12C, not only do you need thicker, puffy layers, but some cold-weather features start to really matter. The kind of features ULers leave off at warmer temps to save weight. A tunnel hood works really well to allow vision while keeping your face warm. Flaps on both sides of the zipper, well-sealed cuffs, inner snow skirt around the waist, etc.

At all temps, most people, but especially Californians (says the 5G SFer), put more and more on their top without putting more on their legs. The cheapest, synthetic-filled nylon bibs (like alpine skiers wear) leverage the rest of your wardrobe tremendously.

Around town, I use one big coat over a t-shirt and flannel-lined jeans. The t-shirt and jeans are enough inside. The single big coat is quick to put on and take off as I leave the house and at my destination. But for outdoor recreation, I want more gradations. That could be puffy pants over expedation-weight polypro UW bottoms and a big puffy coat over a puffy sweater over a synthetic t-shirt on top.

I go with more layers rather than heavier layers. I do a lot of highly active winter activities and when I'm really working hard a thin base layer and my shell is all I need. Sometimes I don't even need my shell. But when I stop, I generally will add a mid layer AND a puffy under my shell, plus a good hat. Layers can be fine tuned so that you stay warm without overheating. An example of my upper body layering would be:
Base layer: long sleeved thin Merino wool shirt
Mid layer: Long sleeved fleece shirt 200-300 weight depending on outdoor temps
Outer layer: Puffy – either down or Primaloft depending on conditions
Final layer: WPB Shell (vents a must- I won't buy a shell without vents)

I'm sort of in between most here. This last winter i did a lot of hiking in a midweight baselayer (usually was a Merino Synthetic blend) with a windshirt, but also brought a light to midweight baselayer as an extra that i often started off wearing as well (and took off as i warmed up enough), and also down jacket with hood (Stoic Hadron anorak) primarily for camp use and to boost quilt or bag temps. Sometimes i also bring a very lightweight silk top, but not for hiking, but for sleeping.

Obviously down and to a less extent synthetic puffies are much warmer for the weight than fabric layers, but i'm digging on the on the idea of combining a predominant merino baselayer with a polypropylene baselayer and wearing the merino underneath as to reduce the odor buildup that is common with wearing polypro directly on the skin. Also, it acts as an extra layer of moisture protection from the outside underneath a windshirt.

Plus, polypro is actually fairly light, and fairly warm for it's weight. All other things being equal, it's going to be lighter and warmer than a polyester fleece, if it's also fleecy in design. (fiber size and arrangement also has a lot to do with warmth retention, generally the smaller the fiber and more haloed or fur like the pattern/arrangement, the warmer it will be because both of these factors trap more air).

"the heavier base layers are certainly warm and fuzzy – pretty cozy looking and reasonably lightweight but sure are bulky. So the thought occurred – is it better to add more, lighter layers rather than carrying one heavier set of layers."

To more directly answer your question, i think you will find that multiple lightweight/thinner layers will be warmer than super thick layers of equivalent weight and bulk.

The why is because many layers trap more air. However, it's important to consider not impeding one's circulation in layering, because impeded circulation will lead to greater coldness and inability to handle cold temps.

Related to what i was saying in the above about polypro, i found this link. If it is accurate, i would say it's kind of impressive.

http://outerbounds.us/what-we-do

Their polypro fleeces are supposedly 20% lighter but at the same time 15% warmer than a similar style and thickness, heavier weight polyester fleece. Still not as good as a puffy, but pretty darn good for a fabric i would say, and something that is going to dry out WAY, WAY faster than a puffy… (and be much more breathable).

Huh… then why aren't all fleece sweaters made from polypro instead of polyester?

I don't know. There use to be a lot of polypro baselayers, and up until not that long ago, the U.S. military used polypro quite extensively, but they eventually dropped it because it has a low melting point compared to some other fabrics. In combat, that is a bad trait. That's why poly-cotton blends are used extensively now. On the related civilian side, it's very easy to ruin a polypro garment by accidentally drying it in the dryer on high for too long. Much harder to damage polyester that way.

Amongst outdoors people, polypro baselayers were quite popular for awhile, but they became notorious for becoming extremely smelly and potentially in quite a short period of time. That is why i advocate wearing thin Merino underneath polypro, to reduce that odor buildup. The merino will act like a bit of a filter layer for the things that cause bacteria growth, like dead skin flakes, oils, etc That stuff is easy to wash out of Merino because it is hydrophilic whereas it's hard to wash out of polypro because it super hydrophobic–that gunk and bacteria build up gets stuck in-between the fibers leading to bad funk fast.

Polypro is not as tough/strong as polyester, so chances are a polyester fleece will last a bit longer than polypro.

These perhaps are some reasons why polypro is not dominating the fleece market, but ultimately, i don't know. Also, things in life and in the market tend to go in cycles. For a long time, wool was relatively unpopular and the newer polyester sportswear all the rage with backpackers etc, but now look at wool and how popular it's become again. People are fickle and most tend to be followers to an extent, markets are fickle, most people and the market is generally easy to manipulate.

Personally, i'm extremely interested in getting one of those polypro fleeces and it doesn't matter to me one whit or not, if it's not mainstream and popular.

Oh, perhaps it's important to consider this as well. Polyester got pushed a lot by marketing forces partly because it's extremely plentiful and cheap to make. Companies/corporations saw an opportunity to make a lot of money without spending a lot. A lot of the polyester that is found in garments comes from recycled PET bottles. Hence, it's been a cash cow for garment corporations. In a way, i think that is a good thing, reusing. But it doesn't mean that polypro is inferior to polyester to use in the outdoors. In some ways, it's much better; lighter, warmer, and even significantly more hydrophobic than polyester.

I use heavier layers. Base, insulation, and shell. Exception in really cold weather is a puffy jacket for rest stops and maybe puffy pants for the end of the day and night.

One last point about polypro. While woven polypro is not quite as tough or strong as polyester, it's still considerably stronger and more durable than lighter weights and non felted Merino wool (heavy, thick, felted wool is actually quite strong and durable, but at quite the weight penalty).

I start with a light wicking base layer next to the skin, using a short sleeve top for hot weather and switching to a long sleeve for cooler and wet weather. The long sleeve keeps my wind or rain shell off my arms.

I can use slightly heavier base layers like Cap2 or Cap3 for shoulder season base layers.

I wouldn't be wearing long johns on the trail unless it was colder (near feezing) or as a base layer under rain pants for all day wet hiking. Long johns are great for camp and sleep. Soft shell pants can offset the point where I might want to use long johns, vs my usual warm weather choice of light nylon zip off pants.

I use R1/Dry Power or Power Stretch for a mid layer for rest stops, camp and sleep. It would have to be below freezing for me to use these mid layers while moving. A wind or rain shell completes the base/mid layer combo. These fleecy mid layers can be worn next to the skin if my base layer is soaked. These mid layer options are great for layering with a rain shell in cold near-freezing rain, which is one of the most miserable hiking conditions I encounter.

Fleece garments like this are heavier and bulkier than light down equivalents, but are much more versatile over a range of conditions and physical activity. If wet weather conditions are involved, the fleece options are superior in several ways. If there is liquid precipitation it is above freezing and the base/mid/shell system is warm enough for rest stops and camp outside of my shelter and sleep system.

For colder weather rest stops I use 100g style synthetic fill tops like a First Ascent Igniter or Patagonia Micro Puff. I don't use down and prefer the mid layer fleece and shell system over the 60g style tops like a Thermawrap or Nano Puff. I feel that the shell layers on theses light jackets is a less breathable duplication of my windshirt and the actual insulation layer provided is quite thin. Where something like a R1 will transfer moisture and remain breathable, I couldn't imagine wearing a Nano Puff under my rain shell while moving.

theres this thing the brits call "faff"

basically is when you have to deal with senseless things, wasting time … like taking on and off multiple layers …

now if one is just prancing around well groomed trails with plenty of places to stop and put down the pack its not a big deal

but if your on a climb you cant always stop and take off this and that layers … or if the wind is blowing all over the place do you want to as its a good way to lose a $$$$$ layer

the other thing is that each time you take off our pack to put on or take off a layer, youre wasting time over and over again

IMO the right way to dress is for your peak activity … then when you stop for short period just zip up … for longer periods pull out that puffy or fleece thats at the top of yr pack and put that on

now i do use down under synth puffies … but the down only comes out in camp so theres not much faff

remember … weight isnt everything … nor thermal efficiency …

especially if you pay the price in faffing

;)

Yup a lot of faff in the first half hour from the parking lot and after a break.

I had a pack that kept dumping the sternum strap hardware, so I spent a few minutes on every break cussing it back into place. I returned it and got back some sanity.

If the trail isn't too rough, I can take off a shell and tuck it into a side or front pocket on a day pack while still walking.

A pocket that can accommodate a small camera saves a lot off fiddling and ups the ratio of photos/trip. Having sunscreen, bug repellent, sunglasses and a bandana in easy reach saves a lot of fussing.

In the old days, taking a big frame pack on and off was a tussle. With modern packs that have belt, shoulder and side pockets in easy reach, we have it made. A pack is a trail office and being able to get to the everyday stuff saves a lot of faff.