what are lightest synthetic base layers

Dead bird phase?

ummm- Capilene 1- top and bottom at 9 oz

MEC T2 Crew Neck

An excellent fabric and garment, IMHO.
6 ounces in Large.

I live in the hoody version.

For bottoms –
MEC T1 Long Johns
Product Number: 5020-395

Phase. 7 ounces total for short sleeved top and bottom.

if you are trying to mimic silk why not just use silk ?

Arcteryx Phase SL – available in a variety of styles. Look for a sale…

Cabela's Power Dry, Polar weight W/ grid inner fleece weighs 10.8 oz. in size Large. Warmest-for-the-weight I've ever seen.

Medium and light weights obviously weigh less. Good prices, great garantee.

I wouldnt go by just weight, if you want some warmth too.

I have 4oz pants, and they have about zero warmth. Literally the cold bites rite in as soon as step outside.

I have 6oz pants, and they are very warm by comparison.

I find fuzzy old polypropylene warmer than capilene, wool, etc.

The new Patagonia capilene 4 bottoms with the grid fleece weighs about 5 ounces, very warm for the weight.

I think that Rohan's (a UK only shop) Ultra stuff might well be the absolutely lightest. 95g long sleeved crew, 80g leggings. Its actually an intriguing fabric as it isn't see through at all and looks/feels fairly 'normal'. Some sort of very fancy knit work with polyester.

Truly not worth the hassle/expense of importing it mind.

TNF certainly at one point did some very light polyproish leggings/tops. Maybe the same sort of weights as the phase stuff?

I find the Craft synth base layers are very light. They are also anti-stink treated. My short sleeve thermal top for example is 80g(large) and they work incredibly well….even though when you first hold it in your hands you think I have been ripped off.

"Looking for recommendations on lightest synthetic base layers."

Summer or winter?

For summer, the Arc'teryx Motus is hard to beat at ~4 oz in a size M, with a UPF of 50+. It also breathes extremely well and dries quickly. For winter, I have yet to find anything better than the new Patagonia Cap 4 Hoody for a combination of warmth and breathability. I'm guessing there are other garments out there made of the same Powerdry HE material that would be about as good, but this is the only one I have used, and I am in love with it. Very well designed, too, typical of Patagonia.

Thanks to all for your suggestions. Art's "if you are trying to mimic silk why not just use silk?" is the right question. I want silk's feel and its light weight (warmth is not the priority in this particular case), but am hoping to get as close as I can to that with the faster drying time, better durability and easier laundering of a synthetic. Silk may still win. Interesting that some of the lightest long sleeve t shirts are lighter than long underwear. I wouldn't necessarily have guessed that.

Best,

Bill S.

whatever is at the discount running store …

those runners often do something highly aerobic called running … which aint usually a feature of backpacking unless its away form a bear ;)

running layers are often very light, quick drying and manage sweat well by the nature of the sport

and because of the size of the market, you can usually find em on clearance

Polypropylene is one of the most thermally AND water resistant (warmest and driest) and yet lightest fabrics commonly used. However, it's weaker than most synthetics and from what i have heard, stinks to high heavens. I don't own and haven't used these at all so i am not speaking from experience on that aspect. I'm a relative youngin and PP is not as common or popular now as it was.

As far as thermal resistance goes, next in line is silk, then polyester not far behind, then wool and acrylic about equal, then nylon, hemp, linen, tencel (the "nano fibril" effect makes it warmer than some of it's cellulose cousins), and then cotton. But there is more to warmth than the innate thermal resistance of the fiber matter itself. There is the shape and structure of the fiber, the diameter size, how it's weaved, etc, etc. Much of the latter relates to how much air it traps. Generally speaking, the finer and more hollow the fiber the warmer it will be, but the scales on wool also helps. Completely round and solid fibers aren't as good as trapping air. Trilobal fibers like silk trap more air than round, etc, etc.

But baselayers aren't used so much for warmth unless you're talking real cold, they are primarily for moving sweat, staying dry, and comfort.

If silk is treated to make it more hydrophobic, then it's not a bad choice in holistic terms of lightness, warmth, stink control, and strength (while it's not the most durable fiber around, it is quite strong for a natural fiber [high tensile strength], but personally i think it's better for a layer over the baselayer for colder weather and high wool blends better for next to skin).

If i recall correctly, there was a field research study done awhile back to see if what one of the original Euro mountaineers who attempted to summit Mt. Everest wore, would be feasible and realistic to do (this particular historical fellow did not make it to the top). I believe i remember reading that he wore something like 7 or 8 alternating layers of wool and silk. What was surprising in the study was that not only was the researcher(s) able to take such temps and conditions in this archaic get up, but it was actually comfortable.

In a lot of ways, nature is still yet wiser and more advanced than man. Especially in the balance area.