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Base layers and the importance of layering

Hiking, trekking and climbing are all activities which involve swings in body temperature. When active, the body produces heat and perspires, and when finally emerging onto a ridge blasted by cold winds, the body temperature can drop to the point of shivering. Sudden rises or falls in body temperature can result in life-threatening issues such as hypothermia. It is therefore extremely important to consider the garments that are worn next to the skin; the base layer. Each material has its own unique characteristics; quick-drying properties, moisture absorbency, elasticity and heat retention. Choosing the material is essentially choosing how you plan on maintaining your body temperature. In this article, Montbell Advising Director, Fumiaki Masaki shares the development history of Montbell's base layers and his own personal experiences on why choosing the right base layer is so important.

Efficient layering

Temperatures can fluctuate wildly depending on the location, elevation and weather (even during the same season). In order to deal with such environmental variations when choosing your clothing it is important to consider the layers you will wear. The basic method is to start layering from the outside in. The outer layer should be able to stand up against the elements, such as wind and rain, and protect the body. The middle layer should retain heat and have moisture regulating abilities. The base layer should cling to the body and maintain body temperature. The trick to layering is to properly understand the characteristics and function of each layer. However, even with a proper understanding, if you wear too many layers, say 4 or 5, you may end up hindering your ability to move. The goal is to minimize layers to preserve your ability to move and choose efficient clothing for each layer.
It is very important that you wear at least a base layer to provide heat retention and an outer layer to protect you from the elements. Personally, I consider middle layers as simply providing support to the functions of the base and outer layers. In particular, since base layers come in various materials and thicknesses, selecting the most suitable base layer to fit the situation will greatly improve efficiency. Starting around November I can go hiking (as long as it isn't too high in elevation, say around 9,800ft/3,000m) with just a thick base layer and an outer layer. Of course, being able to dress like this can be attributed to my hiking style of moving slowly and rarely stopping to rest until I reach my campsite. Since I don’t stop moving, my body is less likely to chill and even if I sweat, I feel that the thick base layer’s ability to retain heat is enough to keep me warm.

Importance of Base Layers

“If you wear cotton on a mountain, you won’t survive” is a phrase that has long been said amongst mountain climbers. It is true that cotton has a pleasant feel and retains heat well, qualities which make cotton great for casual wear. But when climbing a mountain, cotton’s highly absorbent properties can be harmful and when large amounts of perspiration accumulate in your clothing, being unable to dry out becomes a problem. Normally, perspiration is one defense mechanism the body has to cool the body through evaporation. But if your clothing can't dry out and remains wet for an extended period, the body begins to lose unnecessary amounts of heat by conduction through the damp clothing and evaporation. Gradually the body can lapse into hypothermia and if no action is taken, eventually death.

I’ve personally had several bad experiences wearing cotton while climbing. When I first began mountain climbing in high school, I didn’t know anything about wearing wool and attempted to climb in my everyday clothes. I remember many times feeling terribly cold; freezing when the peak’s winds would chill my perspiration soaked in clothing or when getting drenched by rain. Every time my body temperature dropped, my consciousness became hazy, my movements turned sluggish, and everything became a struggle. After a few years of gaining more experience and knowledge, I realized that I had experienced the symptoms of hypothermia. Even thinking about it now I’m really lucky that I didn’t die from hypothermia, which in those days they would have simply said I had "frozen to death." But this really emphasizes just how important it is to choose a proper base layer. I experienced firsthand how vital it is that perspiration be wicked away from the skin and dry quickly.

40 years ago, pretty much the only base layer material for outdoor activities was wool. Though a bit expensive, I’ve even used camel and angora (rabbit) wool. All wool has an excellent ability to control moisture and retains warm air in the fibers to maintain warmth even when wet. The drawback is that all wools have a tendency to shrink.

The reason this occurs is because when wool is exposed to friction or rubbed together after having absorbed moisture, the fibers interlock, crumple and harden in a condition called “felting.” Although wool felt prickly and itchy against the skin, because wool’s ability to control moisture and retain heat was so superior, it was not uncommon for hikers and trekkers to wear very thin wool sweaters as a base layer.

On the other hand, there were base layers made from synthetic fibers such as nylon. Like cotton, these synthetics readily absorb moisture and are made of long filaments. Fabric made using long filaments produces a generally thinner fabric which isn’t able to retain heat, which is why synthetic fibers like nylon aren’t suitable as a base layer. At the time, hikers and trekkers would swear by wool base layers, and synthetic base layers were believed to be undependable.

From natural to synthetic

Wool is one of the best materials for a base layer, but even from the beginning when Montbell was established in 1975, I kept wondering, “There must be a material that can replace wool.” And in 1977, I found one, a fast-drying acrylic fiber called “Orlon.” Because it was a material spun from short fibers, it had a similar texture to wool, and I predicted that it would be good at retaining heat as well. At the same time, a small part of me worried that since Orlon was a synthetic fiber it might absorb water and lower the body temperature in a similar way to nylon and cotton. But after testing it several times in winter alpine conditions, I found it was warmer than I had expected. We used Orlon to create the first base layer from Montbell.

Since Orlon is an acrylic fiber, the fibers themselves do not absorb much moisture on their own. So if you’re thinking, then it shouldn’t wick perspiration either, well, that wasn’t the case. Due to the fabric’s construction, the space between each individual fiber acts to move moisture away from the skin, a phenomenon known as capillary action and commonly referred to as “wicking.” This wicking helps keep the skin dry and comfortable. Because the fibers themselves hardly absorb any moisture, the resulting fabric had superior quick-drying properties. It was soft and comfortable, lightweight, and resistant to odors, making it an ideal material for base layers. As far as climbers were concerned, being able to wear synthetic base layers for alpine climbing was sensational, and this was probably what brought greater attention to synthetic fibers.

The mechanism of quick-drying

A common characteristic of materials that are quick-drying is they don’t readily absorb moisture, as either a liquid (perspiration) or as water vapor (evaporated perspiration). Because the fibers do not hold moisture, the garment dries quickly. However, if the fibers can’t absorb moisture, the skin will be left covered in cold perspiration.
So how is it that a fiber which isn’t able to absorb moisture, is able to move perspiration away from the skin? Each individual fiber is actually processed to better absorb moisture and is able to quickly move perspiration away from the skin. In addition, several individual fibers are wound into a multi-filament and multi-filaments are then wound together to make a thread. Within these multi-filaments are ultrafine gaps between the individual fibers. The perspiration is pulled away from the skin due to a phenomenon called capillary action, more commonly referred to as “wicking.” Wicking works more intensely the narrower the gaps. The perspiration eventually rises to the surface of the material, and gradually expands across horizontally. By spreading itself out over a large area, the sweat exposes itself to air and dries quickly. Thus, a material is said to be quick drying when it doesn’t absorb moisture and is able to wick moisture away from the skin.

However, no matter how superior Orlon’s properties, it didn’t mean that it didn’t absorb any water. Because we wanted a base layer that was quick drying, it was absolutely necessary that the fiber wouldn’t absorb any moisture. In 1982 we considered a polyvinyl chloride fiber called “Chlorofiber” for our base layers. Because Chlorofiber had low thermal conductivity, it had high heat retaining properties and was quick-drying. But Chlorofiber turned out to be a material that was vulnerable to heat, so it was difficult to process and low production output meant that base layers made of Chlorofiber were rather expensive. Fabric made from polypropylene was also available and like Chlorofiber, didn’t absorb moisture. However, drawbacks included its uncomfortable texture on the skin and it tended to attract odors because it absorbed oils.

Polyester is another material often used to make base layers. While polyester does absorb small amounts of moisture, it can be easily treated and processed to give it features to make up for its moisture absorbing properties. For example, modifying the shape of the fibers can improve absorbency and the fibers can be treated to repel odors and prevent the growth of bacteria. In addition, when processing the fibers into a thread, it is easy to improve elasticity. Creating comfortable knits or mixing polyurethane in the weaving process to add more form-fitting elasticity are other possibilities that can be made without sacrificing warmth or restricting movement. Since it can be made available at a reasonable price, it has now become the most popular material for base layers.

Characteristics of each material fiber

The pitfalls of “heat generating” fabrics

While newer and highly functional synthetic fibers continue to emerge, I am commonly asked, “what about a base layer made with ‘heat generating materials’ for mountain climbing?” Because of their ability to “generate” heat, they are frequently seen around town during the colder months. However, we should pay close attention to the type of materials used to make these garments. Commonly made with rayon or acrylate fibers, the common feature these materials share is their ability to readily absorb moisture from their surroundings. While at first these materials do generate heat, once they become completely saturated this ability stops in its tracks. Since these materials generally cannot dry quickly, eventually the saturated material cools and in an outdoor setting, as we learned from the example with cotton, these conditions can lead to hypothermia. The touted heat generating properties of these materials are only effective before you begin to perspire heavily. These garments are perfectly fine for wearing around town, but are unsuitable for activities that cause perspiration, such as hiking, trekking or mountain climbing.

Generating heat by absorbing water?

“Heat generating” materials have recently become popular, but this ability to generate heat is largely related to the material’s ability to absorb water from its surroundings, referred to as “hygroscopy.” The human body is always releasing moisture, either via invisible amounts of water vapor or through perspiration. When a hygroscopic material absorbs water, it does so at a molecular level. This causes a reaction which produces heat. The material’s ability to generate heat is limited to conditions when perspiration is minimal and the garment is dry. When the material becomes wet, it won’t be able to generate heat again until it dries.

The emergence of a “new” wool

Excellent heat retention, exceptional moisture controlling abilities, a comfortable fit, odor resistant even on long expeditions, and doesn’t feel too cold even when wet. These are wool’s appeals. Although long said to be the standard base layer for outdoor activities, its drawbacks include a prickly texture on the skin and tendency to shrink. In recent years, such shortcomings have been overcome and wool has gained renewed attention for use as a base layer. The prickly sensation can be prevented by utilizing ultra fine merino wool, which has a thickness of 18.5 microns (about 1/5 a strand of hair). Felting and shrinking are resolved through various shrink-proofing processes developed by manufacturers. As for being relatively slow to dry, I believe that can easily be solved by simply adding polyester to create a wool blend that would have excellent quick-drying properties.

So which is the better material as a base layer for outdoor activities? Personal preference will play a large part in that decision. However, if you find that you perspire easily, clothing made with fast drying polyester fibers is a good recommendation. If you are planning an expedition or a long stay in the mountains, I would recommend wool for its excellent heat retention and odor resistant properties. In any case, it is important to have a good understanding of the characteristics of each material. As I had mentioned earlier, the base layer is a vital piece of gear for the outdoors and can be the difference between life and death.



- Light Weight Tops & Bottoms

- Middle Weight Tops & Bottoms

- Expedition Weight Tops & Bottoms

ZEO-LINE (Polyester)

- Light Weight Tops & Bottoms

- Middle Weight Tops & Bottoms

- Expedition Weight Tops & Bottoms

Fumiaki Masaki

Fumiaki Masaki was born in Osaka Prefecture, 1952. He is the Advising Director of the Board at Montbell. In 1972, he went on an expedition in Europe and climbed the north face of the Grandes Jorasses and was the first Japanese climber to climb the western face of the Aiguille de Dru. In 1975, long time climbing partner and current CEO of Montbell, Isamu Tatsuno asked Masaki to go into business with him and the two formed Montbell. Over the years Masaki would be involved in product research and development, production and sales. His area of expertise is materials, particularly fabric and fibers.