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Base layers

Your layering system is just like a house, it won’t be sturdy without a firm foundation. In the outdoor activity world, that means you need the right base layer! Resting next to skin, this first piece of clothing is incredibly important in maintaining comfort. Have you ever spent a few hours in a soggy, clingy, icky shirt while hiking? It’s not so comfortable, and you probably felt a little cold as well. So how does a base layer maintain comfort in the outdoors?


The ultimate goal is to move moisture away from the skin to keep you dry. Why is that important? When sweat is left on the skin, it will use energy in the form of heat to turn into water vapor and evaporate away. Essentially, it will steal away your precious body heat. That’s why damp skin and wet layers will leave you feeling chilled, sapped of energy and can lead to hypothermia in some cases (even in summer). We want to avoid that by using a moisture-managing base layer, which will help regulate body temperature and keep you feeling comfy. Base layers also actively retain some heat. Remember though, a base layer is only one part of the “warmth equation”. Middle and outer layers are also incredibly important for staying warm while outdoors.

Montbell offers base layers in two different fabrics and in three different weights. So how do you choose the right one?

1. Select your fabric

Montbell base layers are either made from Super Merino Wool or ZEO-LINE, our proprietary polyester. In general, merino wool provides more warmth for the weight and does a better job of controlling odors. On the other hand, our ZEO-LINE series is faster to dry and more durable. Both fabrics also do an excellent job of managing moisture, just through different mechanisms which are explained later in this guide.

The Strength of Super Merino Wool Base Layers

Body Temperature Regulation

- Retains body heat by trapping large amounts of air between crimps in the fiber
- Will produce some warmth when moisture vapor is absorbed into the internal structure of the fiber
- Continues to provide warmth even when wet
- Middle and Expedition Weight feature a box construction to further retain heat

Moisture Management

- Wool repels moisture under normal conditions, and absorbs it in humid environments within your layering system
- After absorption, wool slowly releases moisture and allows it to evaporate, which reduces sudden evaporative chill
- Small wool scale hold the fabric away from this skin, resulting in a dry feel even when wet (it will wet out eventually though)

Odor Control

- Absorbs moisture and bacteria to offer a high level of odor-resistance

Next to Skin Comfort

- High-quality merino wool fibers are highly elastic and deliver a soft, smooth touch (forget those itchy wool shirts!)
- Carbon fibers are added to provide anti-static properties


-Polyester is blended in to enhance durability and provide long-lasting use

Easily Wash at Home

-Treated to allow for easy washing at home (remember to use a mild detergent)

Where Super Merino Wool excels:

- Long days spent in colder temperatures
- Low intensity activities with less sweat
- People with generally cold, dry and sensitive skin


Moisture Management

- Effectively pulls moisture away from the skin, then diffuses it across the fabric where it quickly evaporates to leave you and the fabric drier
- Actively dries while you're on the move, so you don't get chilled from damp layers while stopped
- We apply a special wicking agent to pair with polyester's natural quick-drying properties to further enhance moisture management

Body Temperature Regulation

- Traps air between the fibers to retain heat
- Dense knit fabric further seals in body heat
- Pulls moisture away from the skin to prevent you from feeling chill due to moisture evaporation
- Middle and Expedition Weight feature a box construction to trap additional body heat

Odor Control

- Offers odor-resistance with a silver ion anti-bacterial treatment

Highly Durable

- Polyester is highly durable and long-lasting

Next to Skin Comfort

- Features a soft touch and excellent stretch to follow the body's movements
- Carbon fibers are added to provide anti-static properties

Where ZEO-LINE excels:

- Activities with a lot of “stop and go”
- High intensity pursuits that produce a lot of sweat
- When quick-drying is more than heat-retention

2. Select your fabric weight

Montbell offers both fabric types in Light, Middle and Expedition Weight. The optimal fabric weight for you will largely depend on climate. This will include many variables such as season, elevation and where you're headed. For example, ZEO-LINE Light Weight might be best for trail-running on a moderate trail in early spring. However, hiking on the same trail at a slow pace in December could make Middle Weight a better option. We've outlined some recommended usage scenarios below for each fabric type and weight to help you get a general idea.

Light Weight:

Our light weight layers are designed for year-round use in generally warmer conditions. From spring, summer and fall, all the way to mild winter days or when at low elevation, these layers provide great use 12 months a year.

Super Merino Wool

(85% wool + 15% polyester / Fabric weight: 125 g/m²)

Within the seasonal conditions listed above, are you mainly doing lower output activities that produce less sweat? Here are some examples: hiking (low intensity) versus trail running (high intensity), backpacking (low intensity) versus fastpacking (high intensity). If that's the case, then merino wool will be a great option. It will regulate moisture while keeping you warm and comfortable even at high elevations in summer, and its comparatively longer drying time won't be an issue because you'll be doing "less sweaty" activities. Headed out for multiple nights? Wool's superior odor resistance will help you stay fresh and fight off some of that stink even on an extended trip in the backcountry.


(100% polyester / Fabric weight: 120 g/m²)

However, do you enjoy fast-paced, high output activities such as trail running, fast packing? For these sorts of activities, ZEO-LINE may be a better option with its faster drying time. Also, variables such as high temperatures or steep elevation gain can turn low intensity activities (hiking, backpacking, etc.) into sweaty excursions where ZEO-LINE may be a better match. While you're on the move, it's working to wick moisture from your skin and allow it to quickly evaporate from the surface of the fabric. This will help you stay drier and prevent that chill feeling of sweat slowly evaporating off of your skin.

Middle Weight:

Our Middle Weight base layers are also great for year-round use, only in generally colder conditions. Think backpacking in late fall with some early snow, trail running on cold winter days, or climbing above tree line in summer. If you want to use your base layer further into winter and additional warmth and thickness is needed, then Middle Weight is the way to go. These layers provide enough warmth to be used for winter sports such as ski touring, snowshoeing and snowboarding.

Super Merino Wool

(85% wool + 15% polyester / Fabric weight: 175 g/m²)

Same as the Light Weight, the Super Merino Wool Middle Weight is better for low intensity activities (hiking, backpacking, etc.), just in colder temperatures. Where Light Weight would be perfect for summer backpacking, Middle Weight may be better suited if you're going into high elevations in summer or doing a trip in late fall or early winter. These layers are also great for activities like resort skiing and snowboarding in winter, where the chairlift is doing all the work, and the exertion and sweat output on the ride down is relatively low.


(100% polyester / Fabric weight: 165 g/m²)

Likewise, ZEO-LINE Middle Weight is better suited to cold temperatures when compared to its Light Weight counterpart. Even on a chilly winter day, once you start running, quickly gaining elevation, or making dynamic movements, you'll find yourself heating up. The quick-drying and moderate heat-retention of ZEO-LINE Middle Weight will help keep you comfortably warm while effectively managing the sweat you put out during strenuous activity. These properties are also well suited for highly aerobic snow sports like cross-country skiing.

Expedition Weight:

These base layers are purpose-built for winter activities in incredibly cold conditions and frigid temperatures. Think multi-day mountaineering expeditions in the middle of winter, backcountry skiing when it's below freezing, and other similar activities where a lack of warmth isn't an option. *Exp. Weight is designed for extremely cold conditions and will most likely be excessively warm in more temperate climates. If you need something for spring, fall or summer, choose a Light Weight or Middle Weight.

Super Merino Wool:

(79% wool + 18% polyester + 2% nylon + 1% polyurethane / Fabric weight: 220 g/m²)


(100% polyester / Fabric weight: 250 g/m²)

When talking about Expedition Weight and fabric, it's best to talk about together, because both provide the necessary moisture management and warmth retention, just in different ways. These weights are also essentially broken down by the intensity level of the activity. Let's say you're planning a multiday snowshoe trip in the beginning of January, or going cross-country skiing in cold, snowy, windy conditions. These aerobic activities will generate sweat even in below-freezing temperatures, so quick-drying ZEO-LINE would be an excellent choice. However, for activities that of lower intensity, Super Merino Wool will be better suited because it offers that extra bit of warmth while also managing the comparatively less amount of sweat. That could be technical winter alpine climbing where the pace is slow, winter wildlife observation and other similar activities.

3. Increase your knowledge!

How merino wool regulates your body temperature

Merino wool possesses a natural ability to create a degree of warmth through a phenomenon called "heat of sorption". This occurs when moisture vapor is absorbed into the fibers, and is then transformed from gas to liquid. This results in a release of heat in the process. Merino Wool fiber also contains a large number of crimps, which traps a large amount of air to deliver an excellent level of heat retention. Together, these two properties provide an incredible ability to keep you warm by regulating your body temperature.

How merino wool regulates moisture

A microscopic look at the surface of an individual fiber reveals a protective scale structure. The scaly outer layer repels water, while the core remains highly absorbent. Under normal conditions the hydrophobic scales shut moisture out. However, as humidity increases due to body heat and perspiration, the scales open slightly to allow the sweat-absorbing core to be exposed. In fact, merino wool has an amazing capacity to absorb moisture up to 35% of its dry weight into the fiber core! The scales further play an important role by holding the fabric away from your body. This results in a dry feel even when the fabric is carrying some moisture. Commonly, these scales are removed in the shrink-resistance process. At Montbell, we have been able to perfect an anti-shrink technology which leaves the majority of these scales intact, allowing you to safely wash your base layers while also enjoying the natural characteristics of wool fibers.

How merino wool limits odor

The unique chemical structure of wool absorbs and locks down odorous substances such as ammonia gas and acetic acid gas to block and reduce odors. The complex nature of wool fiber also allows us to create a moisture-absorbent fabric that keeps the skin drier. Without a warm, moist place to thrive, odors have a hard time building up, which means you smell better longer.

How zeo-line dries quickly

We apply a special hydrophilic treatment to polyester fibers which contain a hydrophobic core (Think moisture absorbent outside and non-moisture absorbent inside). What does that mean? The core won't hold water, but the surface of the fibers will, helping to quickly move moisture away from your skin to the fabric surface where it can evaporate. Furthermore, small space between the fibers act as capillaries, actively drawing perspiration away from the skin to further promote quick-wicking properties.

On a larger scale, moisture is absorbed and diffused over a large area of the fabric where it can evaporate. With perspiration quickly moving from skin to fabric, and fabric to atmosphere, you get to feel dry and warm even during high-intensity activities.

How ZEO-LINE retains heat

Air is trapped between the ultra-fine polyester fibers, retaining body heat and providing warmth. Ceramic is also kneaded into the fibers, which further improves heat-retention. How though? The ceramic takes heat emitted by the body and turns it into far-infrared rays. These infrared rays are radiated back and absorbed by the body where it is converted back into heat, becoming additional warmth for you.

We take long filaments of crimped fibers and surround that with short fibers to create impressively elastic fabric. This also creates an additional layer of air that further promotes heat retention. (ZEO-LINE Light Weight ONLY)

How ZEO-LINE reduces odor-causing bacteria

To control odors means to control odor-causing bacteria. The polyester fibers receive a treatment which features silver ions. These silver ions actively limit bacterial growth, which results in an odor-control system to help you stay fresh for longer in the outdoors.

How Box Construction enhances heat-retention

(Super Merino Wool/ZEO-LINE Middle Weight and Expedition Weight models only)

On our Middle and Expedition Weight fabrics (both Super Merino Wool and ZEO-LINE) we utilize a gusset-like box construction, created with two fabric layers connected with bulkheads. The result is high degree of heat retention delivering an impressive level of warmth.

4. Features found in Montbell base layers

Along with fabric type and weight, Montbell base layers come with numerous features to enhance comfort and maintain mobility.

Slant-Tec Armhole

Eliminates seams on the shoulder and promotes stretch around the armhole.

Spiral Slant-Tec Cuff

Delivers stretch and an excellent fit.

Zip End Guard (high neck models)

A small flap at the end of the zipper protects your chin and face. Also a quick note that base layer tops with half-zips are great for managing temperature because you can open them up to vent excess heat and moisture.

Seamless Design (Super Merino Wool EXP. Weight)

Made in a circular knit, seamless design to further enhance comfort.

Flat Seam Technology

Eliminates bulk along seams and promotes a smoother touch.

Drop Tail Design

Covers the waist even when leaning forward.

Thin Elastic Waistband

Provides a good fit and allows for comfortable layering.