The Summary and Recommendations page provides a short synopsis of the principles of layering, makes some suggestions as to how a legacy synthetics kit could be improved by adding one or more layers, and lists several standout products as well as discussing guidelines for the assembly of layering arrays in various conditions.

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Layering Index



Base Layers: Synthetic and Merino

Field Shirts, Pants, and Outerwear

Legacy Synthetics

Summary and Recommendations

Product Descriptions

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The principles of layering clothing apply to both warm and cold weather. In warm weather, you can improve temperature regulation and moisture transport by using more than one layer, and in colder weather you gain these advantages and can also improve flexibility of the clothing to temperature variations, allowing you to remove or add layers to maintain a comfortable body temperature. Merino wool is more efficient at temperature regulation than synthetics, synthetics are more efficient at moisture transport than Merino. You can combine the materials to increase performance, taking advantage of the strengths of both.

Layer categories are separated into base layers (next to the skin), mid layers (added atop the base layers to add warmth without adding bulk), insulating layers worn in colder conditions under the shell, and the outerwear (hard shell or soft shell). These layers are available in several weights, and often midweight base layers are used as mid layers, and heavy base layers can be used as insulating layers. Packability should be considered when selecting a kit. When I am not carrying the pack, I carry a LowePro Utility Bag at the back of my belt to carry layering elements (see the photo at the bottom of the page). It is handy to be able to load a number of layering elements into a small pouch that can attach to your belt or pack for easy access.

Many people have collected a variety of legacy synthetics over the years, and due to the durability of synthetics, many are still serviceable. Often, these earlier synthetics either had no antimicrobial treatment or early versions of current antimicrobial treatments which deteriorated over time, and built up odors with each use, contributing to the well-known "synthetic stench". Current antimicrobial treatments are permanent and far superior to earlier treatments (or no treatment) at combating the growth of bacteria which cause odor, and Merino is naturally antimicrobial, thus the addition of these materials in strategic locations within your array can reduce this problem. The augmentation of your current array with selected current materials can also improve moisture transport (wicking) and thermal regulation characteristics.

Although using selected materials within your existing kit keeps costs down and will improve performance, replacing legacy synthetics with a carefully selected kit can improve comfort next to the skin, moisture transport (wicking), thermal regulation (allowing you to wear fewer layers across a wider range of temperatures), flexibility of use across a wider temperature range, and packability. You will also very likely be able to carry a more effective kit in a much smaller pack (especially since you will not require nearly as many changes for synthetics retired due to objectionable odor).


Moose at Sunrise Floating Island Lake 0293

A female moose stands atop a small hill near Floating Island Lake
and watches the sun rise over northern Yellowstone National Park.


If you only buy one new thing, I recommend that you consider getting a couple of pair of Merino briefs. I cannot say enough about the comfort of Merino underwear. It is as soft next to the skin as cashmere, wicks well, never feels clammy even when wet, is the most comfortable in both cold and hot weather in my experience, regulates temperature far better than synthetic or cotton, and they resist odor for days (although you still want to rinse them out now and then). While cotton is cooler in very hot weather, it can saturate easily and takes forever to dry, thus the Merino is better overall even in very hot weather.

The most effective single augmentation to a legacy synthetic kit is the addition of a Merino layer between two synthetic layers, which will improve temperature regulation as well as allowing the same number of layers to work to a lower temperature, or allow you to reduce the number of layers to operate within the same temperature range and either carry fewer layers, or have additional changes for those which become objectionable due to odor buildup. Also, you may want to consider adding a Merino T-shirt as your next-to-skin layer. As you have probably noticed, the layer closest to your skin is the one which builds odor most quickly, and you can wear a Merino layer next to the skin for up to five days without rinsing before it builds odor (rinsing it now and then increases the time you can wear it without odor buildup). Merino is most effective at temperature regulation when it is next to your skin, so this will also improve the thermal regulation of your kit.

Replacing an entire set of layers will allow you to take advantage of the synergy of various types of layer arrays. While both current synthetic and Merino arrays will do a very good job of moisture transport and heat regulation, Merino is better at heat regulation and synthetics are better at moisture transport. You can take advantage of the strengths of the two materials by mixing the materials strategically within a layering array.

Featured Recommendations

This group is composed of those standout products which I would not want to be without. If you are looking for something which fits into one of these categories, you cannot go wrong with one of these products. Some of these products are so versatile they traverse multiple categories.

Smartwool NTS Light 195 Boxer Brief
(the WoolX X303 was a close second to this superb brief).

The Smartwool NTS (next to skin) 195 Boxer Brief had the best combined finish, fit and feel of all four of the Merino boxer briefs. The fit of the WoolX is also superb, and the feel was close (after it was washed the second time). I cannot say enough about the comfort of Merino underwear. It is as soft next to the skin as cashmere, wicks well, never feels clammy even when wet and regulates temperature far better than other underwear. Merino underwear is the best single acquisition.

While the Smartwool NTS 195 Boxer Brief was the best of the boxer briefs in this dissertation, Smartwool no longer offers them (the NTS 150 Boxer Brief is still in their line, however). This makes the WoolX X303 the best choice of the boxers in this list.

WoolX X302 Outback Lightweight 170 g/m T-Shirt and Patagonia Capilene 1 Silkweight T-Shirt (tie)

These are both superb core layers. They both feel wonderful against the skin, and they both wick well and work synergistically with layers above, improving moisture transport and temperature regulation. The Patagonia wins the wicking contest and the WoolX wins the temperature regulation contest until the temperature exceeds 80 degrees. The WoolX is far better in cool to cold temperatures, and the Patagonia is far better in warm to very hot temperatures. They both do very well in the cool to warm region. Pick your poison, or do what I did and get both.

If you would prefer to have a single T-shirt to act as a core layer to cover the range between 50 and 95 degrees, select the Patagonia Merino 1 Silkweight T-Shirt. The surface is rougher against the skin than the two above, but it is cooler in the upper regions of this temperature range than the Capilene 1 and more comfortable at high temperatures than the WoolX X302, and although it does not add much warmth it greatly improves the temperature regulation and wicking abilities of a layer array. From more recent tests, I have determined that the most comfortable short-sleeved Merino T-shirt for use in very hot weather is without a doubt the Icebreaker Aero Running T-shirt, a 90% Merino, 10% polyester 120 g/m featherweight (nearly as soft as the superb WoolX Outback, wicks as well and dries as fast as the Patagonia Merino 1, and highly breathable).

Patagonia Merino 2 Zip-neck (or WoolX X507) and Patagonia Merino 3 Hoody

This Merino/Capilene 2-layer array is a brilliant combination. As a pair, they wick and regulate temperature very well, and they are quite breathable, which extends the capability of the array as the temperature or activity level rises, although at the lower end of their temperature range, a light breeze can make them chilly (see the note below). The high collar of the hoody can be zipped up and doubled over to form an excellent neck gaiter when necessary, and the anatomically-shaped hood fits the head closely and covers all but the nose, frontal cheeks and eyes. The Merino/Capilene pair do not wick as well as a comparable Capilene array, but they regulate temperature far better. The combined fabric thickness is about the same as the WoolX X507 midweight, but the combined 2-layer pair are warmer, superior in moisture transport and temperature regulation, and more flexible as the temperature or activity level rises (you can remove the hoody when required by higher temperatures or activity levels), although the WoolX X507 midweight provides about 75-80% of the performance at roughly half the cost. This pair constitutes the most flexible and best performing mid-layer (see the note below), and have the most comfortable neck seam design.

Speaking of the WoolX X507, it also makes a superbly synergistic companion to the Merino 3 hoody, and due to the softer, more comfortable texture of the WoolX Merino, it is more often used in combination with the Merino 3 Hoody than the Merino 2. The Merino 2 is most often used between the MH Integral Pro and the Merino 3 zip-neck or Smartwool 250 midweights.

WoolX X302 Outback Lightweight T-shirt, X507 Explorer Midweight 1/4-Zip, and X-305 Base Camp Lightweight Hoodie

The release of the WoolX X305 Base Camp Lightweight Hoodie (June 2015) has created the softest, most comfortable and most flexible layering array in this list. The WoolX X305 Base Camp hoodie can be worn alone, as a core base layer, or along with one or more underlying layers. Along with the X302 T-shirt the hoodie is comfortable into the mid 50s, and adding the X507 midweight would take you into the low 40s depending on activity level. All three of these garments are extremely soft and comfortable next to the skin (best of all of the Merino I have used), and any of these can be worn alone or together in various conditions. The WoolX Base Camp hoodie has extra long gusseted sleeves with comfortable reinforced thumb holes and a denser jersey weave than the Patagonia Merino 3 hoody (the different spelling is theirs), and while the WoolX is thinner it blocks wind as well. The single-layer WoolX hood design is not as good in cold weather as the multi-layer semi-balaclava Patagonia hood, but the longer sleeves with reinforced thumb holes are more comfortable and afford better coverage. The combination of the X507 Midweight and X305 Hoodie are warmer and offer better temperature regulation than the Patagonia Merino 2+3.

Overall, I prefer the WoolX array for its greater comfort in cool to warm weather, but the Patagonia Merino 3 hoody is better as an interstitial layer in a cold weather array than the WoolX X305 hoodie. The WoolX hoodie also makes a superb core layer for use underneath the Patagonia Merino 3, and is often used in this configuration.

WoolX X704 Blizzard Heavyweight 400 g/m 1/4-Zip Top

The WoolX X704 1/4-Zip Top can act as a heavyweight upper base layer under an insulating layer in very cold conditions, an insulating layer in cold conditions, or a top layer in cool to mild conditions without the bulk of a typical insulating layer. It is also quite useful as a top layer in milder conditions when used with only the Merino T-shirt. This is the top you want to put on when starting out in the morning before generating body heat, or when your body begins to chill as the activity level or temperature drops. It can be used in such a wide range of conditions that the only reason not to take this top is when the temperature would be above its useful range (about 65 degrees).

Patagonia Capilene 4 Thermal Weight 1/4-Zip Hoody

The Patagonia Capilene 4 Hoody packs to a 5" x 5.5" cylinder and is extremely lightweight, yet very warm when covered by a layer which traps air. The large gaps between the fleece blocks in the grid allow the material to breathe very well (and let in any trace of breeze). It can be used in mild to warm weather with simply a T-shirt (or alone), and it works synergistically with layers worn below. At lower temperatures, when used along with an underlying layer array, the Capilene 4 hoody adds breathable warmth. When covered with a shell and/or another layer it gets even warmer. The extreme flexibility of this hoody both as an insulating layer and as a base layer makes it one of the most versatile tops I have used.

WoolX X509 Explorer Midweight 230 g/m Bottoms

The WoolX X509 midweight bottoms have a high-contoured back rise which provides extended coverage regardless of your movement or position and does not slip down, and along with the double-panel gusset allows for a wide range of movement. For those who have climbed in long underwear and experienced the typical “plumber’s exposure”, this will mean a lot. These bottoms are quite warm by themselves (warmer than silkweight and midweight synthetics together), and the Merino is soft and comfortable next to the skin. They are the go-to bottoms in cold to mild conditions.

Kuhl Krux Long Shorts

In my humble opinion, the Kuhl Krux long shorts are the best hiking shorts ever designed. They are 16" shorts with articulated knees that fall at the upper calf, providing knee protection which is extremely useful when you are on the rock, in dense forest, or bushwhacking through high grass. The durable lightweight fabric is their “berkuhl” cotton/nylon blend which dries quickly. They have a gusseted crotch for extreme mobility and a superb pocket design, with two deep hand pockets, two side-entry zippered thigh pockets, two velcro-patch back pockets and a 3D thigh pocket for accessories. The interior is covered with mesh, and the rear, thigh and hand pockets act as an incredibly effective venting system. These are far and away the most comfortable shorts that I have ever used in temperatures over 90 degrees.

Kuhl Radikl Pants

The highly flexible Radikl uses a woven cotton/nylon exoskeleton (68% cotton, 29% nylon, 3% spandex) with knit stretch panels (88% nylon, 12% spandex) in strategic locations to allow for unprecedented mobility. The Radikl offers the appearance, strength and performance of traditional lightweight hiking pants and the flexibility of a stretchy climbing pant. For those who do not like to climb in shorts or knickers, the Radikl are the climbing pants you have been trying to find for years. They are very comfortable in hot weather, and the fit is full enough to allow you to wear lightweight and midweight (or single layer heavyweight) thermal bottoms and still have full mobility.

The Radikl pants are an innovative design using a lightweight 5.2 oz./yd woven exoskeleton with knit stretch panels down the outside of the legs, under the knees, surrounding the rear patch pockets, and composing the entire gusset down to the articulated knee darts. The Radikl are very comfortable pants for hiking, approach and climbing, although the exoskeleton material is quite a bit thinner than the material used for most of the long shorts and knickers I typically climb in (about the same weight as the Krux), and you have to be careful with your knees. The material withstands light abrasion.

Kuhl Raid Softshell Pants

The Kuhl Raid softshell pants are more stretchy than the Radikl above, being made from a 5.1 oz/yd, 85% nylon, 15% Spandex breathable softshell fabric with a brushed interior and a smooth exterior with a DWR finish. The Raid pants will repel snow and light to medium rain (in all but torrential conditions they will allow you to forego the use of hardshell rain pants), and they are comfortable across a wide range of temperatures: from the high 40s (calm) or 50s (windy) to over 85 F. without a base layer. The Raid has 6 pockets (2 hand, 2 rear, a 3D pocket on the right thigh, and a small drop-in pocket on the left thigh), each with reverse-coil zippers to keep the contents dry, and an elastic blousing drawcord on the cuffs to keep snow and rain out, as well as to keep the cuffs out of the way when climbing and rock scrambling. The Raid pants are a good choice for cool to warm weather hiking, bushwhacking and climbing, and for general purpose outdoor use in a wide range of weather conditions, as are the slightly heavier Kuhl Destroyr (6.1 oz/yd) at a lower temperature range.


Sandhill Crane Take a Bow HS0443

A juvenile Sandhill Crane acknowledges his appreciative viewers as he finally achieves
balance on the ice at sunrise on a brutally cold January morning at Bosque del Apache.

For me, there are several key criteria for selection, and as with any long-term decision, you balance the relative importance of the various criteria for selection against particular needs and the available budget. Without any specific order of importance, my overall selection criteria are: comfort, flexibility, and durability of materials; efficiency of moisture transport and heat regulation; an intelligent design with regards to essential item storage, extremity coverage where necessary, and synergistic interaction with layers around their intended position in an array; and reasonable conformation to body shape without loss of long-term comfort or mobility. You have to assign priorities and try to select items which best fit your needs in a variety of environments.

In my case, I ended up with a variety of items in each general category, many of which work best with certain other items, thus creating several different types of sub-arrays. These sub-arrays can be used as components to build arrays for various different environments. In your case, you may find it best to carefully consider the possible variations in climate you will encounter and select items which will cover these specific conditions. When you add items, consider how they will work with existing items to increase the effectiveness of existing sub-arrays and/or make a more effective transitional element between components.

Layering Arrays

In previous iterations of this Summary page, I have listed a number of different multi-layer array options based on type and density, and listed the approximate low end of the temperature range based on the activity level and amount of acclimation to low temperatures, as well as the amount of hood and hand protection. As the large number of possible combinations of synthetic, Merino and mixed arrays can become extremely confusing, what I am going to do this time is give a series of general guidelines that can be applied to any set of layering garments.

It is to your advantage to have a good working knowledge of how comfortable you are at different temperature ranges with different levels of activity, and plan your array density based upon the lowest temperature you will encounter at the lowest activity level. Using a larger number of lighter layers to achieve this density will allow you to easily fine-tune the array based on changes in temperature, activity level, and body heat, and the air trapped between several lighter layers will allow the array to be more effective in temperature regulation than an array of the same density with fewer layers. Keep in mind that how you handle heat and cold is dependent upon your body type, percentage of body fat, circulation, and other factors. Evaluate your tolerance to cold weather and your typical activity levels, and plan your kit accordingly.

At low activity levels with light wind, I am typically comfortable with a 550-650 g/m array in the mid-to-high 40s Fahrenheit (at the lower end of that density range in direct sunlight); 700-800 g/m from the high 30s to low 40s; 900-1000 g/m around freezing; and 1100-1200 g/m in the low-to-mid 20s. These array densities are all based on use without a shell... you should experiment with your shells so you know what the effect of adding a windshirt, light shell or heavy shell will do when used atop a given array.

In my experience, having a Merino layer as a core layer next to the skin is more comfortable under a wide range of conditions, and more effective at regulating temperature. Synthetic layers wick moisture more effectively than Merino, and the surface is also more durable, thus in situations where the surface layer can be easily damaged, it is often advantageous to place a synthetic layer on top. In a multi-layer array, using a Merino layer as an interstitial element can improve the temperature regulation, and using a synthetic layer as an interstitial element can improve moisture transport. Generally, in my experience a Merino array of a given density is both warmer and far more effective at temperature regulation than a synthetic array, but there are significant advantages gained by using certain types of synthetics as interstitial elements. For instance, using the Patagonia Capilene Thermal Weight Hoody as an interstitial element between a light Merino element and an element which blocks wind greatly increases moisture transport and adds a significant amount of warmth due to the air trapped between the fleece grids... removing the wind-blocking element allows the highly breathable grid fleece to release air and excess heat rapidly.

Regarding pants, there are two general ways I tend to approach the bottom layers: either with cotton/nylon blend pants augmented with one or more base layers, and shorts for warmer weather use, along with hardshell full-zip pants for protection from torrential rain; or a layering system based on softshell pants with a DWR surface, composed of lightweight softshell pants atop midweight softshell 3/4 pants plus 2-layer (OTC + short) socks to cover the temperature range from the 30s to about 90.

The softshells can handle light to medium rain well... anything heavy and I break out the full-zip hardshell pants. For temperatures below freezing I will most often revert to multiple base layers plus the Raid softshell, but I sometimes add the WoolX midweight bottom to the two-layer softshell if shorts will be required later in the day. In sub-zero temperatures, in a heavy wind, or when standing in very cold temperatures I add the full-zip Marmot Precip hardshell pants. The softshell array is the most flexible option for cold to warm temperature uses, but in mild to hot weather where a long pant is required, cotton/nylon is best in my opinion. In warmer (and drier) situations where climbing may be necessary, sometimes a cotton 3/4 climbing pant is used as a base layer under a cotton/nylon blend outer pant, allowing a rapid change in response to heat or a need for climbing.

With all of that said... what is nice is:

the ability to select a kit which is the most flexible for the conditions that you are likely to encounter.

Having the option to select components which offer the most benefits in the specific sub-conditions,
yet which operate synergistically with other component sets, allows you to attempt to cover all anticipated
situations, while hopefully being able to maintain the least weight and the smallest possible packing volume.

The primary component groups (core, mid-layer, insulation layer, light shell, heavy shell) may not all be necessary, and sometimes it makes sense to split a primary component group into two complementary items. When components work well with those in the groups around them, you can more easily eliminate a component on one side or the other in the field to adjust to changing conditions. I often find myself splitting either the mid-layer or the insulation layer into two components, especially in conditions where I will not need a heavy shell.

I select very different types of arrays for very cold to mild conditions; cold to warm; or chilly to hot. I generally use Merino for core and mid-layer, mixed synthetic and Merino for insulation layers, and synthetic top layers.

In a long-term effort to find "the right stuff" to address the goal of augmenting existing legacy layering garments and acquiring multiple synergistic modern arrays, I have tried a number of interesting products, including past-year products acquired at a discount in the effort to get the most performance for the money. The target was to attempt to explore as many options as possible to establish criteria for informed decision-making, while focusing on the needs of the person who would primarily be carrying gear in belt-mounted cases and pack, as most of the people I know who are not professionals do not use a tactical harness to carry equipment. This method of carrying gear makes the use of most lofted insulating layers (and most other outerwear which covers the waist) a problem, which is why there are none listed in this dissertation. For those who do not carry gear in this manner, using a modern lofted mid-layer instead of two base layers which can be tucked in may be a better option.

In the process of selecting gear, as there is a limit to the number of arrays and combinations required (which I exceeded in my zeal to provide myself with options, and outline potential methods of combination for readers), I bypassed several extremely interesting items. Those items which remain of extreme interest and should be considered are:

Patagonia Merino Air base layers: available in crew, hoody and bottoms, the Merino Air base layers are an innovative design made of a stretchy lofted Merino yarn blended with Capilene fiber. The lightweight garments (195 g/m, 205 g/m and 175 g/m respectively) are highly breathable, are gaining an enviable reputation for quality and warmth, and are exclusive to Patagonia.

Polartec Power Wool: a hybrid two-layer fabric made by bonding a Merino interior layer to a synthetic exterior layer. This innovative approach optimizes the performance of a garment by combining the natural odor-fighting properties and warmth of wool with the wicking properties and durability of synthetics into a multi-layer fabric whose layers work together synergistically. Some highly interesting garments made from Power Wool include the Mammut Trovat Pro and Under Armour Charged Wool. Garments made from Polartec Power Wool could very likely eliminate the need to carry synthetics to protect Merino garments from damage when used in the forest or in abrasive environments.

Arc'teryx Konseal Hoody and Mountain Hardwear Desna hoody: these Polartec grid fleece light jackets with Hardface exteriors are both designed to be worn under a belt or harness (the MH is also available in a mock-neck). The Mountain Hardwear Desna has two vertical zipped hand-pockets which terminate above the harness or belt, and while it is a full-zip it can easily be used with belt-mounted gear. The Arc'teryx Konseal is a half-zip with a chest pocket and the most versatile hood arrangement I have ever seen, with a highly stretchable Phasic AR panel that can be deployed as a neck gaiter or balaclava and a form-fitting hood. Both are designed with gusseting and articulated patterns for mobility, and have extra-long sleeves equipped with thumbholes.

I hope this dissertation has given you a good feel for the benefits and use of various materials, and how to best outfit yourself for various conditions in the mountains. Obviously, even though I have explored a number of products and outlined quite a few combinations, there are a vast number of options out there. I hope I have given you enough information to apply the principles to your unique requirements so you can make informed decisions which allow you to select gear which will be right for you.

—   Ron Reznick


Ron at Glacier Point 6360

Taken by Scott Peck, one of my students, during a photographic training session in May
overlooking Half Dome and Tenaya Canyon in Yosemite National Park just before sunset.


Layering Index



Base Layers: Synthetic and Merino

Field Shirts, Pants, and Outerwear

Legacy Synthetics

Summary and Recommendations

Product Descriptions


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