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Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers

An in-depth comparison of the properties of wool and synthetic fabric for base layers yielded some surprising results.

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by | 2006-07-25 00:00:00-06

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 1
Alan backpacking in a clown shirt on a sweltering day in the Appalachians. Backpacking Light manufactured three hybrid testing tops that were half wool and half synthetic. Hybrid shirts were sent to staffers Alan Dixon, Will Rietveld, and Don Wilson. Each of us used a wool-synthetic top for several months of intensive field testing over the winter and spring. Early on in the testing process, Will dubbed these “clown shirts.”


Fifty years ago nearly every outdoor kit included a wool shirt. Ten years ago, wool had been banished in favor of lighter and more comfortable synthetic base layers. But wool is back. With finer yarns, wool base layers are now marketed as comfortable next to skin. At the same time advances have been made in synthetic fabrics that further improve performance and address some of their shortfalls. This healthy competition has saturated the industry with new technologies and performance claims regarding wool and synthetic base layers.

In this article we will take an independent look at the properties of these fabrics. We ran a series of field and laboratory tests to evaluate field comfort, drying times, fabric weights and moisture wicking performance. In the process, we revealed some unexpected performance properties and learned a few things about how these fabrics compare in a diverse range of field conditions.

The Purpose of a Base Layer

Base layers have two fundamental objectives - temperature control and moisture control. The two are closely interrelated, but for purposes of this article we will equate temperature control with insulation. All base layers perform this task reasonably well, and relatively little separates the wool and synthetic fabrics.

By its very definition a base layer is not designed to be your primary protection against wind, rain or intense cold. When conditions go bad, you should pull your outer layers out of your pack. But under many conditions it may be that your base layer is your only top garment for the vast majority of your hiking day - providing sun protection, some warmth, moisture management, and a bit of modesty. This is both a weight saving (potentially fewer garments) and a time saving (less clothing adjustments/changes). Since you could potentially wear this garment 24 /7 its comfort is a significant contributor to your overall comfort and well being on a trip.

Moisture control is where a base layer can really make a difference in maintaining comfort in the field. A base layer should help keep you warm when it is cool, and cool when it is warm. As your next to skin layer, it is primarily responsible for keeping built up moisture away from your skin. Base layers use a variety of techniques and fabric properties to help you stay dry and comfortable. They will wick water away from your skin. They will disperse moisture across a wider area to facilitate drying. They will store water and keep you cool with evaporative cooling. When soaked, a base layer should dry quickly.

The series of tests we describe here were designed to help us compare the relative performance of a sample of commonly used wool and synthetic base layers. But before we jump into the test results, let’s review the structure and properties of wool and synthetic fabrics.

Wool Base Layer Fabrics

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 2
Photo 2. Wool and synthetic fibers: standard wool (top), merino wool (center) and synthetic polyester fiber (bottom). Photo courtesy of Ibex.

Wool base layers have made a significant splash over the past few years primarily as a result of the improved comfort level of wool as a next to skin fabric. New softer wool fabrics have been developed and a growing number of manufacturers are now producing wool base layers. The critical change has been the use of Merino wool in modern outerwear. Merino wool has a softer feel than traditional wool, with fiber diameters of less than 20 microns (see Photo 2). Traditional wools are typically at least 32 microns, and frequently up to 80 or more microns. This explains why old wool fabrics felt like Brillo Pads against your skin. The thinner fibers of Merino wool are more flexible, hence softer and more comfortable against your skin. A few manufacturers are now producing merino wool fabric with fibers less than 18 microns in diameter, and efforts continue to produce affordable base layers with ever more comfortable fabrics.

To understand the properties of Merino wool fabrics you must first understand the structure and properties of wool fibers. Unlike synthetics, which have a uniform composition inside and out (i.e. it’s a hunk of plastic that may be shaped), individual wool fibers have an exterior scaly sheath, enclosing bundles of interior fibers (see photo 3). The surface of each fiber is hydrophobic (repels moisture), helping to repel water off the surface of the fabric.

Because of the complex internal structure of wool fibers, and the fact that the interior portion of the fiber is hydrophilic (attracts moisture), water can be absorbed INTO the fibers of a wool fabric, whereas in synthetic fabrics water is only held in the spaces between individual fibers since the fibers themselves do not absorb water. Merino wool fibers can absorb approximately 30 percent of their weight in water. Synthetic fibers themselves will not absorb any water. This means that wool fabrics will hold more moisture than synthetics and will take longer to dry. But in a wool fabric the water is stored away from the surface, and consequently a wool garment may not feel so clammy next to your skin when wet.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 3
Photo 3. The internal structure of a single wool fiber is a complex matrix consisting of numerous bundles of sub-fibers. Water can be absorbed into this internal matrix and then released again. Image courtesy of Ibex.

This ability to store moisture within the structure of the fabric gives wool some of its most useful properties. As your body warms up, the moisture stored within the fabric will begin to evaporate, cooling the air between your skin and the fabric. This same cooling effect will also hold for synthetic fabrics, but the additional moisture held within the wool fibers will prolong the cooling effect. So long as the wool is not completely saturated, its surface will stay dryer than a slightly wet synthetic layer, and it will not feel cold and clammy against your skin.

An interesting part of the wool story is that as wool absorbs water, the internal structure of the wool changes, and the fabric actually releases heat in a process known as the “heat of sorption”. Although the total energy involved in this process is small in comparison to other processes such as evaporation, this heat of sorption may help to raise your skin temperature and make you feel warmer. Depending on the conditions this may or may not be beneficial. In cold weather where you may have built up a little sweat from skiing or snowshoeing, this reaction could help keep your skin warmer. Note: There is still debate about the significance of this phenomenon. The discernible effect, if any, is mostly the comfort of the fabric against the skin. The actual heat generated is too small to have a significant warming effect for your body.

Of course, wool clothing is also well known for resisting the build-up of body odor that is prevalent in many synthetic base layers. Wool is naturally resistive to the bacterial growth that can make some synthetic clothes bring tears to your eyes after a few days or weeks in the backcountry. Synthetics claim to be closing the gap with new treatments to reduce stench. While synthetics have improved their resistance to odor build-up, the consensus among the Backpacking Light staff is that wool is still ahead by a significant margin. A wool trail shirt may be your only civilized option for sitting in a restaurant after the trip, assuming you don’t have a chance for a shower and change of clothes before you dig into that hot meal.

For many people another positive for wool is that it’s a natural, renewable resource. Merino sheep are sheared once per year, and wool fibers will naturally break down over time. Wool easily absorbs natural dyes and can be processed with limited use of harmful or toxic chemicals. Some manufacturers are now processing wool with minimal chemical processes.

Synthetic Base Layer Fabrics

Many of the original synthetic base layers were polypropylene, but polypropylene has a very low melting point and requires a bit of care while washing. The melting point of polyester (260 to 270 degrees C) is much higher than polypropylene (165 degrees C) and therefore requires much less care laundering, especially in a hot drier. Note: wool too has improved. The newest merino wools require much less care than their predecessors and can be put in the drier without shrinking. Polypro also had a reputation for body odor build up. Modern polypro has improved upon both care and odor problems but its reputation persists. For example, many polypro laundering instructions still call for a cold wash and drip dry. Many synthetic base layers, including most of the high-end ones, use polyester fabrics for their ease of care and improved odor control. Other problems with polypropylene include poor abrasion resistance and poor "memory” (shape retention). The advantage to polypro is that it is a lighter fiber than polyester so you could potentially make a 40% lighter garment. (Note: The density of polypropylene (0.91g/cc) is much lower than that of polyester (1.38 g/cc). Polypropylene floats in water while polyester sinks.) Another advantage of polypro is that it absorbs almost no moisture. Finally polypro is typically a less expensive fabric. Thus polypro is still used as a base layer fabric, but primarily in lower cost garments.

Woven - as opposed to a knit fabric as is typically used in base layers - nylon fabric is often used in warmer conditions for sun blocking, but few base layer (i.e. wicking) garments are made of nylon. Since most high-end base layers use polyester we will focus on polyester base layers in this article.

The key advantages of synthetics over wool are that they are lighter, dry faster and are considerably less expensive. As we will show in the tests below, the lightest synthetic base layers are still significantly lighter than the finest wool. Because the individual fibers do not absorb water, synthetics will remain much lighter than wool when both are saturated. And the synthetics will dry more quickly too. Last but not least, synthetics are much less expensive - typically 30 to 50 percent less than wool products with similar function.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 4
Photo 4. Two examples of polyester synthetic fibers with added surface complexity. Textured surfaces improve moisture movement and drying times; and consequently reduce odor buildup. GoLite’s C-Thru fabric (left) and MontBell’s Wickron fabric (right). Images courtesy of GoLite and MontBell.

Synthetic fibers have made numerous advances over the years, many of them mimicking the best properties of wool, but still maintaining the benefits of synthetics. Paramount among these are advances that help synthetics to move moisture more quickly across the surface of individual fibers, helping to disperse moisture, improve drying time, and keep moisture away from your skin. This is typically done by adding texture to the surface of the synthetic fibers, or changing the cross-sectional shape of the fibers, or applying a chemical finish. This texture or finish increases surface complexity, making it more hydrophilic. The objective of these shape modifications is to speed movement of water along individual fibers, away from your skin and dispersing the moisture closer to the outer surface where it will evaporate more quickly. Examples of these fibers are Patagonia’s Capilene (treated, roughened surface), Marmot Qwick (hydrophilic chemical treatment) and GoLite C-Thru (modified fiber shape).

Many synthetic garment manufacturers have taken steps to reduce the build up of body odor in their clothing. This odor problem is especially prevalent among synthetic base layers which are next to your skin and kept warm and moist as you wear them - perfect conditions to grow a festering pool of stinky bacteria. An ultralight backpacker might wear the same base layer for a week, significantly increasing bacterial breeding opportunities and stench. Wool is inherently anti-bacterial. Its protein based structure (keratin) provides natural protection against odor producing bacteria.

Synthetic garment manufacturers use numerous techniques to reduce bacteria buildup in synthetic base layers. Most of these involve applying anti-bacterial coatings to some or all of the fibers. Many treatments use silver ions which are applied or woven into the fabric. One approach is to impregnate silver ions directly into the yarn. Another approach embeds the silver ions on the surface of the fabric, making more effective use of silver’s anti-microbial properties. An example of a silver embedded fabric is VisaEndurance, by Milliken. VisaEndurance is used by many manufacturers, including Mountain Hardwear in their Extend Featherweight base layers.

Comparative Field Testing of Wool and Synthetic Base Layers

One way to compare the performance of wool and synthetic base layers is to create hybrid garments. Backpacking Light spliced and sewed three hybrid tops that were half wool and half synthetic. We chose Smartwool Microweight for the wool side and Patagonia Lightweight Capilene for the synthetic side. The insulating properties and field use of these fabrics are comparable, which made them a good pair for comparison of wool versus synthetic field performance.

Each tester used a hybrid wool-synthetic top for several months of intensive field testing over the winter and spring. Our goal was to get the top out into a variety of conditions, with a focus on conditions that challenged the performance of the fabrics. That meant using the tops in vigorous aerobic activity and a variety of temperature and weather conditions. We tested the tops in temperatures ranging from well below freezing in the Colorado mountains to 90 degrees in the Sonoran desert spring and 95 degree late spring days in the Northeast. Weather conditions ranged from wet/cold winter days in Colorado, humid spring conditions in the eastern US, and dry spring heat in the Sonoran desert. We all received occasional dubious looks while wearing these shirts, or were teased mercilessly by friends and family. Early on in the testing process, Will dubbed these “clown shirts” - and henceforth we referred to them by that moniker. They were definitely a conversation starter when we met people in the backcountry.

Field Test Conditions

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 5
Don on a winter training run, Saguaro National Park, Arizona.

Don made a habit of wearing his top on all of his trail runs and conditioning hikes during winter and spring. That usually meant a vigorous climb or run of 6 to 12 miles with elevation gains of 2000 to 4000 feet. Most of the time Don overheated while climbing, and the top was important to keeping him dry and cool. A few times conditions were cold enough to keep him cool or cold, but that was the exception in his testing. Don is a longtime user of synthetic tops, only recently spending more time in wool base layers.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 6
Will in his clown shirt on a conditioning hike in southern Colorado.

Over a four-month period Will put his pride aside in the name of science, and wore the infamous shirt out in public (gasp!) on a total of 31 day trips while snowshoeing, cross-country skiing, and day hiking. Will wore it either as a base layer or an outer layer, depending on the temperatures, which ranged from 30 to 65 °F. On several occasions he pushed hard to build up a good sweat on his favorite conditioning hike - a 1.5 mile 1500 foot 45 minute charge up a local mountain without stopping. (Will says, “Don’t snicker, that’s good for me!”)

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 7
Alan on the spectacular Angel’s Landing trail, Zion National Park, Utah.

Alan tested his shirt in the cool spring conditions of Washington, DC, with temperatures in the 30’s to 50’s °F, and also had it out in the western US for a late spring trip to southern Utah. Finally, Alan tested his top on a muggy 95 °F backpacking trip in the Appalachians. Note that Alan’s top is a short sleeve model, while Will and Don used a complementary pair of long sleeved tops. All three tops were made from the same fabric combination.

Cool Weather Performance

All three of us tested the tops in cool conditions, from below freezing up to about 50 degrees. Alan had intense bicycle and trail running workouts in 30 to 50 degree temperatures with relative humidity around 80 percent. Under these conditions, Alan noted that the Capilene side spread moisture out over a larger area and dried more quickly than the wool side. This held true for all of our testing, in all conditions. But despite absorbing more water than the Capilene side, Alan found that the wool side was warmer and more comfortable on the skin in cool temperatures. The wool side felt especially warm when cooling off after an intense workout while the Capilene side felt decidedly chilly. But the Capilene dried much faster. An hour after one of Alan’s workouts, the Capilene side was dry while the wool side was still damp. It took the wool side approximately another hour to dry.

Don’s cool weather testing was done under drier conditions. On long uphill trail runs in cool weather, the Capilene side stayed drier, but when wet, Don also found the wool side more comfortable. The Capilene side allowed more wind to pass through to the skin, helping Don stay cool even when the climbs got serious. In cool, comfortable, windy conditions, Don found the performance difference negligible, as both sides were dry and comfortable. The more humid conditions of Alan’s testing may help to highlight the differences between the fabrics.

Will’s experience in cool conditions was interesting. His comment on the field performance difference between the fabrics was, “nada!” In the cool conditions of Colorado, he found no significant difference between the two fabrics, despite putting them through a long series of field tests. In Will’s words, “When worn as an outer layer, I built up a good sweat climbing hard, stood in the wind at the top, got chilled on both sides, put a shell on over it, and dried out quickly without further chilling. When worn as a base layer, both fabrics effectively dispersed moisture and dried out fairly quickly. I tried hard to distinguish a difference, but I can’t honestly say I could detect a difference.”

Synthetic (Capilene) Dries Faster

All three testers found that the Capilene fabric was faster to dry. Don soaked his top in a creek and wore it for a downhill hike on a 58 degree morning. Almost immediately the wool side felt warmer. After 5 minutes of hiking, the Capilene side began to be noticeably drier than the wool side. The Capilene side was dry after 20 minutes of hiking, while the wool side reached a similar level of dryness at 35 minutes. Will ran a similar test and found the drying time of the Microweight wool side about 50 percent longer than Capilene [more on Will’s tests below.]. Alan’s field experience for drying times was similar (except he exercised for a long time at an intense level and used his own sweat to soak the shirt.).

Warm Weather Performance

Don wore his top on numerous warm weather trail runs and conditioning hikes. Under all of these conditions, Don detected little difference in the performance of the two fabrics. He was surprised at the comfort level on the wool side in these conditions. Both fabrics were reasonably comfortable for Don, even when exercising in hot weather. (Note: Don is a desert dweller and others may find these fabrics uncomfortably warm under hot weather conditions.)

Alan tested his top on a 30 mile backpacking trip in the Appalachians with muggy weather, 95 degree days and many, many thousands of feet of climbing. While Alan preferred the synthetic side for comfort, it was not by a large margin. The wool side’s lack of stench in the hot weather was a real plus.

Both Don and Alan noted that the synthetic side was a bit cooler due to its lighter and more air permeable fabric. This was especially true under breezy conditions, where the synthetic side was noticeably more ventilated and cool. While Don found both fabrics reasonably comfortable in hot weather stress tests, he would not opt to use a base layer under these conditions. His preference for warm weather hiking is a loose fitting, well ventilated top such as the RailRiders Adventure Top (a woven nylon fabric with mesh side inserts). Don also notes that wool has made good strides in comfort against the skin, but still is “definitely not cotton.” Alan had no issues with wool’s next to skin comfort, even in extremely hot weather.

There is consensus that untreated synthetic garments build up a significant stink, but what about wool? Our testing provided a good opportunity to test both fabrics under identical conditions. Don did not wash his clown shirt all winter and spring. After every sweaty workout he threw it in the drawer with his other base layers. Four months later, Don can conclusively state that the Capilene side does indeed stink. The wool side is nearly stink free with some of the minimal odor possibly from loitering near the Capilene for so long. Alan also did not wash his garment for at least two months with similar results. The wool side was nearly stench free while the Capiline side was not fit to be worn withing 50 feet of civilized company (the neighbor’s Rottweiler thought it was great!). So while synthetics may have improved, wool is still superior to untreated synthetic in fighting off odor buildup. [Will was more hygienic and washed his clown shirt.]

Laboratory Tests of Select Wool and Synthetic Fabrics

To get a more controlled look at the drying rate and fabric weights of wool and synthetic fabrics we ran a soak and dry test on five leading fabrics. These tests were a simple look at drying rates under low humidity conditions and are most useful as a comparative indicator. Field drying times will vary widely based in humidity, temperature, wind, aerobic activity, and other clothing worn. Two synthetic fabrics were tested, GoLite DriMove and Patagonia Lightweight Capilene. The three wool fabrics were Ibex 17.5 micron, Icebreaker Superfine, and Smartwool Microweight.

Table 1. Fabric Specifications
Fabric Fabric type Swatch Weight (g) Fabric Weight g/m2
Patagonia Lightweight Capilene 100% polyester 12 133
GoLite DriMove 100% polyester 10 111
Ibex 17.5 micron Merino wool 14 156
Icebreaker Superfine Merino wool 18 200
Smartwool Microweight Merino wool 14 156
Note: Fabric samples were 30 cm by 30 cm. Due to relatively small swatch sizes and rounding error, weight per meter squared has approximately 10 percent (plus or minus) error.

The test procedure was a simple soak of the fabric swatches in room temperature tap water for 20 minutes. Samples were removed simultaneously and allowed to drip for 1 minute. Each was then weighed every 5 minutes. The test was run outside in the shade with temperatures of approximately 65 degrees F. Relative humidity was approximately 40 percent. Fabric swatches were laid flat on concrete while drying.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 8
Figure 1. Drying time summary. We verified that synthetics dry faster. The two synthetic fabrics were dry after 65 minutes (Patagonia Lightweight Capilene) or 75 minutes (GoLite DriMove). The wool fabrics took 90 to 100 minutes to reach their dry weight.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 9
Figure 2. Weight of fabric after soaking. When soaked, synthetic fabrics are lighter than their wool counterparts, even for a very absorbent synthetic like DriMove.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 10
Figure 3. Percentage of water absorption in comparison to dry weight (X times dry weight) for selected synthetic and wool fabrics. This figure shows that there is not as much difference in percentage of water absorption between synthetics and wool as we initially believed. Taking out the anomaly of the very absorbent DriMove, the values ranged between 3 and 4x for all fabrics. GoLite DriMove, while the lightest fabric, absorbed the greatest percentage of its dry weight in water (10 g to 48 g is 4.8x) but was still the second fastest drying fabric. This underscores the ability of synthetics to dry quickly even with large amounts of water.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 11
Figure 4. Detailed drying rates (base data) for selected synthetic and wool fabrics.

An Alternate Test - Drying Rate When Worn (Will Rietveld goes a step further)

All of us observed that in the field the synthetic side dried faster. But exactly how much faster? Swatches of fabric can tell us only so much. Obviously, the drying rate of a whole garment on a warm body would be a better indicator of field performance.

Will went a step further to get a more precise measurement of the drying rate of the clown shirts while on the body. He devised a simple but ingenious test to measure the drying rate of both sides of the wet shirt while on his body. Will measured the temperature of a wet clown shirt (on his body) with an infrared thermometer. He did this for both the synthetic and wool side at 5 minute intervals.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 12
Test procedure: Clown shirt soaked for 4 hours, then run through the spin cycle in a washing machine to remove excess water. Will then put it on the shirt and measured the temperature of the wool and polyester sides with an infrared thermometer at 5 minute intervals. Ambient conditions 70 F and 15-20 percent relative humidity. Results: Synthetic (Caplilene) dries at 30 min. Wool (Smartwool Microweight) dries at 45 min.

Note that the shirt quickly warmed up from Will’s body heat after he put it on. It then stayed around a constant 80 degrees (because of evaporative cooling) for about 20 minutes. Finally, the fabric warmed up to a steady state of 88 °F indicating the fabric had dried (no moisture left for evaporative cooling).

It is always nice when lab tests and field tests agree. Don’s soak the shirt in the field and then wear it, with a subjective assessment of dryness was 20 minutes to dry for the synthetic side and 35 minutes to dry for the wool side. This is within reasonable agreement with Will’s on body tests. Don’s faster drying times are likely due to his exercising in the field (more heat generation and warmer skin temperature versus Will’s at rest skin temperature and heat generation) and that fact that Don was moving and therefore creating some wind aided drying. Don has long legs, is in excellent shape and hikes a good clip. Don’s subjective measurement in dryness versus Will’s temperature based measurement of “dryness” may also account for slight differences in perceived drying time. That is, the shirt may feel dry even though it has residual moisture.

Will also used the same infrared thermometer test method to see how much faster a shirt dried when worn versus on a hanger. Surprisingly, wearing the garment only decreased drying time by 15% for both fabrics (at least at an ambient temperature of 70 °F and low humidity of 15-20%). As temperatures drop and relative humidity increases, we would assume that the difference in drying time would increase between a shirt on a hanger and on a warm body.

Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers - 13
Test procedure: Clown shirt soaked for 4 hours, then run through the spin cycle in a washing machine to remove excess water. Shirt then put on a clothes hanger and the temperature of the wool and polyester sides measured with an infrared thermometer at 5 minute intervals. Ambient conditions 70 *F and 15-20 percent relative humidity. Results: Synthetic (Caplilene) dries at 35 min. Wool (Smartwool Microweight) dries at 55 min.

In Will’s whole garment tests and the lab fabric swatch tests, Smartwool took 57% and 53% longer to dry respectively. That is, the percentage difference in drying rate between Capilene and Smartwool was the same even thought they used very different test methods - Will’s a full garment, a washing machine spin cycle which removed more excess water and dried on a hanger (both sides exposed) versus the lab tests with fabric swatches that were not wrung at all but only allowed to drip for 1 minute and laid on concrete (single side exposed).


General Note: Differences between wool and synthetics for both water absorption and drying times were not as earth shattering as we initially thought.

Choices we make for base layers should be based on conditions we hike in, and properties of fabrics. But even under similar conditions personal preference plays a big role. Each of us has different comfort levels for each fabric. Some people can’t wear even the softest wool fabrics without breaking out in a rash, while others cannot tolerate the stench of wearing a synthetic garment for a week, and still others hate the clammy feeling of synthetics. Whatever your personal preferences, we hope the information provided here will help you make more informed choices about your base layer.

Tester’s Personal Conclusions

The following are our personal conclusions from this series of tests and field testing.

  • Wool is significantly better at resisting buildup of body odors than most synthetics - even the improved ones
  • Wool feels warmer and less clammy on the skin when damp
  • Wool takes approximately 50 percent longer to dry than synthetics (range 40 to 60 percent). This was consistent across the board under a large range of conditions - in lab tests of fabric swatches, whole shirts on hangers, shirts on warm bodies, and actual in-field performance of shirts wet with sweat and shirts intentionally saturated with water.
  • In our soak test, the difference in water absorption (x increase over dry weight) between wool and synthetics was less than we initially believed. Approximately 3x dry weight for synthetics versus 4x dry weight for wool.
  • Synthetic fabrics wick moisture out faster over a larger surface area. This may in part contribute to their faster drying times but also to a chilling effect in cool and especially windy conditions.
  • Synthetic fabrics are lighter than wool for comparable warmth.
  • Many synthetic garments are significantly less expensive than wool.

Wool and synthetic base layers preferences of Backpacking Light Staff


  • A wool top serves as a combination shirt and base layer for most trips. Wool’s lack of stench and next to skin comfort (less clammy and feels warmer when wet) are major reasons for his selection. That wool is a minimally processed natural fiber also appeals to him.
  • In torrentially wet environments like the rain forests of the Pacific Northwest or New Zealand’s South Island, the lightest synthetic base layer like Capilene would be the preferred choice. Low water absorption and quick drying times are the major reasons.
  • In serious cold weather mountaineering a synthetic top like a Patagonia R1 hoodie. Warmth, flexibility for varying conditions, minimal water absorption and faster drying are reasons. Even in a cramped mountaineering tent, stench and next to skin feel are distant considerations.
  • On shorter trips in very warm conditions, a thin synthetic base layer may be selected. In desert conditions a thin nylon top like a RailRiders Adventure Top could be the most desirable.


  • In cool or cold, dry weather wool is the preferred choice.
  • About 80 °F synthetic or wool base layers (knit fabrics). Like Alan he is more apt to wear a thin woven nylon shirt (conventional fabric) like a RailRiders Adventure Top.


  • Will did not have a significant preference between wool and synthetic base layers. This may underscore the fact that under many conditions there are only minor performance differences between wool and synthetic base layers. It may also be that Will is an easy going guy with few idiosyncrasies about his trail clothing. Or it may be that Will actually washed his clown shirt a few times during testing. (Will eventually sided with the Smartwool. Not for its performance but for its better fit - longer sleeves and torso length.)


"Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers," by . (ISSN 1537-0364)., 2006-07-25 00:00:00-06.


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Comfort and Moisture Transport in Lightweight Wool and Synthetic Base Layers
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Michael Davis
(mad777) - F

Locale: South Florida
Re: Re: Re: Re: Re: Merino wool, Icebreaker, and New Zealnd on 11/29/2007 11:09:49 MST Print View

John or Forrest,

Can you post the weight (and size) of your Conquest Hoodie?


John Haley
(Quoddy) - F

Locale: New York/Vermont Border
Re: Re: Re: Re: Re: Re: Merino wool, Icebreaker, and New Zealnd on 11/29/2007 12:59:40 MST Print View


I answered that question in my original post. The Conquest hoodie, in size Large, weighs 22oz. BTW, the hoodie is quite a bit larger than the Bodyfit 200 base layer. The Bodyfit 200 in a large fits both my top and legs like skin (I'm 6'1" and 186#), the hoodie in 320 EXP is more like a normal sweater fit. It does fit easily over the base layer.

Michael Davis
(mad777) - F

Locale: South Florida
Re: Re: Re: Re: Re: Re: Re: Merino wool, Icebreaker, and New Zealnd on 11/29/2007 13:43:41 MST Print View

Thanks John,

Sorry about asking to repeat the weight.

It's getting bad when I can't remember back just 2 posts! I'm glad they display my name when logged into this website so I don't forget who I am. :-(

BTW: I'm exactly the same height & weight as you so fit should be the same.

Thanks again,

john griffith

Locale: Southeast U.S.
correct way to measure baselayer performance on 07/03/2008 18:21:24 MDT Print View

I can usually expect a plethora of keen insights from the forum comments after the articles. For once I'm disappointed at the lack of depth. All you guys are talking about is weight, warmth, drying time. I'm a total capilene guy. There is a certain amount of joy to be had when being out in the dead of winter with a hiking partner, and after a few days of putting in hard miles with windshirt/raingear on top of your baselayer, being the one that clearly smells the worst inside the tiny little tent that you don't dare ventillate because it's ten degrees outside. Does nobody else get this? Capilene rules!

LeRoy Schmeling
(leroys) - F
Wool - water absorption on 01/30/2009 15:26:04 MST Print View

I camp in the dampness of the Boundary Waters area of Northern Minnesota. Wool has become my BL of choice. I've gotten good deals on Terramar products.

Re water: I started treating my garments with the wash in water based DWR products and really like the result. There is less water absorption, they shed light showers and dry quicker.


James Moughan
Re: Why didn't BPL do this: on 02/01/2009 22:11:37 MST Print View

I think these values are very interesting. They show that each fabric takes almost the same time to loose a gram of water in the fabric. With an average time of 1:53 min and a 9,4% spread. Most interesting is that the smartwool shirt dries actually 1 second faster than the patagonia shirt.

2 years late ッ but this is a really good catch. When hiking, drenching your base layer should be rare if you control venting and such, so merino seems clearly superior.

David Shepherdson
(shepherdsond) - M
Re: Why didn't BPL do this: on 02/25/2009 13:05:14 MST Print View

Yes, great catch. This is a key variable IMO.

I like the feel and performance of wool baselayers and the sustainbility but my concerns are cost and durability. I have polyester baslayers that are 15 years old and still going strong whereas I just had to retire a Smartwoll microlight base layer after 4 years of average use (too ma ny rips and tears). My wife suggested that it might last longer if it was not dried in a dryer so I am trying that for my icebreaker replacement. I also have another durability question. I find that most of my wool sweaters end up with moth holes in them long before they wear out, is the same true for merino baselayers? I assume it is...

Mitchell Keil
(mitchellkeil) - F

Locale: Deep in the OC
Wool and the Sun on 08/27/2009 14:06:11 MDT Print View

Has anyone, including the testers and staff anything to say about the SPF of Wool vs Synthetics. I have worn both during many hikes. I prefer the wool and have used an Icebreaker LS 200 crew as my go to shirt/baselayer in everything from 30degrees to 90degrees in the Sierras and the San Gs near LA. I am very sun sensitive and from my observations whether I am wearing a high SPF rated synthetic or my wool I seem to get the same result: no over exposure to harmful solar radiation. But I can't really find anything online or from the manufacturers of wool apparel that indicates wool's sun protective qualities.

Any comments or citations?

Einstein X
(EinsteinX) - F

Locale: The Netherlands
Re: Comfort and Moisture Transport.... that's odd. on 08/27/2009 14:42:46 MDT Print View

Now this is an odd article! I read it already three years ago, as you can also see in the post date of the "Companion forum thread to" post. Even though being an old (but good) article it popped up in my iGoogle's BPL RSS reader as a fresh and new article. Or it least I was of the opinion that the 5 newest articles that BPL publishes will appear in my iGoogle page. So how come this one popped up??


John Davis
(Bukidnon) - F
Old article showing up as new on 11/01/2009 03:23:33 MST Print View

Same here, Eins.

But I'm glad because this was a good read. Your 2007 post is interesting and possibly calls for an answer from those who tested the swatches. Strangely, the conclusion drawn from your calculation is completely at odds with my experience. After a run I feel an urge to get out of a merino top within 30 seconds of getting back home because the heavy weight of cold sweat feels horrible against my skin. In the only synthetic top I have left, after ending the run, I can keep it on long enough to prepare a recovery drink and run a bath.

No one has mentioned getting a hot, sweaty back under a rucksack. I was one shouldering long before reading about it in Beyond Backpacking because I can sweat enough over a couple of days of backpacking to cause nappy rash. I find merino particularly unpleasant against the skin of my back when a day's walking has turned uphill and aerobic. It really itches when warmed up a bit.

Merino has numerous, clear disadvantages so why do I prefer it? On my last Pyrenean hike I had a Capilene T-shirt and a Smartwool long sleeved top. I had thought that the T would be the garment I walked in and the merino top would be for evenings. That is not what happened. The T-shirt became so stinky within half a day that I could not stand it. (One of the 2006 posts mentions this problem. I wish I'd read it back then.) The merino went on and stayed on day after day without becoming unpleasant.

There must be something physical and measurable, apart from lack of stench, which accounts for my preference for merino. Perhaps it's to do with the drape. Merino feels more classy, somehow.

By the way, synthetics do wear away. Mine became thinner and thinner till all that was left was a net of fine fibres. The seams on synthetic tops have always had a tendency to carve away at my delicate skin, particularly round the armpit, and this becomes much worse once the top is a bit worn.

Best wishes.

david plantenga
(dplant) - F
Synthetics & Wool on 02/03/2010 05:19:06 MST Print View

Interesting detailed article.

Did I miss "cost"?
Synthetic "T" shirt about $8 to $10
Wool "T" shirt about --------?

Off subject comment: First thing I thought of with Trail Runner Don in the Desert ... Rattlesnake Magnet ...?

Happy Trailz

Steve Arlowe
(sarlowe) - F
High Altitude Reflected Sun - Compression Shirt or Merino Baselayer? on 06/21/2010 15:06:39 MDT Print View

Great info here! Anyone have additional comments about using a long sleeve merino baselayer to block sun and keep cool, especially in more or less low-humidity conditions? I took a white Zensah compression shirt on a Kilimanjaro trek in 2007, and just last week to Muir on Rainier. The compression shirt is fantastic at blocking/reflecting the sun and acting almost as an air conditioner. Any sweat evaporates immediately, keeping me nice and cool. And since it's a compression shirt, this is the case for every square inch. No baggie sleeves to trap air - which seems to me would allow heat build up and impair wicking. So the only drawback on the white compression shirt in that setting is, of course, the stench. Zensah uses an antimicrobial treatment. But while the stink is reduced (and kind of a different, slighlty less pungant odor) than your typical untreated wicking synthetic, it's still there, still pretty objectionable. Meanwhile my Smartwool midweight that I also wore off and on all week has no discernable odor. So now I'm looking at Rapha's white merino baselayer or Smartwool's microweight in silver. I gather merino's wicking is better, but evaporation is not as good. Is the evaporation enough poorer that I'll go from feeling air-conditioner-like properties to feeling like I'm wearing a thin but soggy insulating layer? Anyone have any experience with the newer generation UnderArmour heatgear? It claims antimicrobial properties - does it fight stench as well as merino? Thanks!

Edited by sarlowe on 06/21/2010 15:07:31 MDT.

Paul McLaughlin
(paul) - MLife
Re: High Altitude Reflected Sun - Compression Shirt or Merino Baselayer? on 06/21/2010 21:35:49 MDT Print View

I have used lightweight wool long johns as a baselayer/sunscreen, up to about 12,500 in the sierra in early May on a ski trip - worked great. Have not used a wool top in the same way, as I don't have one in a light enough color. I found the wool bottoms to be nearly as cool as wearing nothing, and they definitely wicked, evaporated and kept the (very intense) sun off just fine.

Steve Arlowe
(sarlowe) - F
Re: Re: High Altitude Reflected Sun - Compression Shirt or Merino Baselayer? on 06/22/2010 09:53:30 MDT Print View

Thanks Paul! Good to know. I suppose it's a question of finding something that works in a certain range of conditions. A merino baselayer might fail in hot/humid conditions (while a synthetic compression shirt is able to keep up evaporation-wise). But I suppose on a glacier with ambient air temps of 20-40 degrees yet brutal sun, the merino's evaporation performance will be adequate to give me that effect.

Thomas Rayl
(trayl) - MLife

Locale: SE Tx
Drying times on 11/22/2013 10:07:34 MST Print View

I don't know if anyone will see this as it's 3 years+ since the last post.

I noticed the discussion points which seem to indicate that differences in drying time are apparently most closely related to difference in water-holding capacity of the different materials. In the tests, the swatches were soaked. So... If my shirt (or whatever) is soaked, I'm not just going to throw it over a bush as is...I'll WRING IT OUT FIRST. It would be interesting to see a follow-on which takes the soaked test swatches, wrings them out to see how much water they will "mechanically" release, then compares drying times.