Expedition Essentials: The Perfect Base Layer

6 December 2023

Almost every expedition kit includes base layers. As the name suggests, this is your initial layer and, in some cases, the only layer. They could be socks, gloves, underwear, T-shirts, and more.

A base layer is meant to be snug against the skin, creating a secondary skin layer on your body. Some may prefer wearing these loosely, but it’s more about personal preference than performance.

There are several key functions that base layers serve:

  • Moisture wicking
  • Thermal insulation
  • Sun protection
  • Comfort
  • Odour resistance (for the garment, unfortunately)

Base layers are often marketed as suitable for all environments, with solutions for nearly every context. Exercise caution with manufacturers’ claims as they may not always hold true.

Moisture Wicking

One of the most commonly highlighted benefits of base layers is their ability to wick moisture or sweat. This process involves drawing sweat away from the skin into the garment or layers of garments.

It’s important to note that WICKING IS NOT EVAPORATING! Wicking removes moisture from the skin, ensuring that evaporation occurs within the garment(s) and likely on the outer surface. This function helps the garment remain dry. Imagine the impact of wearing a soaking wet T-shirt in freezing conditions, especially when you stop generating heat through exertion.

However, these processes are designed to prevent you from cooling down. While perfect for cold environments, they might not be ideal for hot ones.

Consider this: in a hot environment like a jungle where evaporation at the skin is already limited, would you choose a tight base layer? There are varied opinions on this, but loose-fitting clothing allowing air to flow over the skin could enhance evaporation and convection. Loose fits might also provide better defense against insect bites and stings.

Thermal Insulation

The insulating properties of base layers vary based on fabric type, engineering, and how you wear them.

A thin, skin-tight polyester base layer offers limited insulation and might even reduce the thermal protection of fine body hair. Conversely, thick merino fabric provides significant insulation.

Fabrics can be engineered in diverse ways, from plain fabrics to mesh and waffle knits, carefully designed to manipulate thermal properties. Research specific base layers, considering both manufacturer information and independent reviews.

For instance, companies like Brynje produce mesh garments that may not seem particularly insulating. Yet, their mesh design significantly reduces moisture contact with the skin and increases the trapped air volume around the body. When paired with suitable mid-layers or windproof clothing, these can offer greater thermal performance than simple woven fabrics.

Sun Protection

Depending on your attire, a base layer could serve as your primary defense against the sun. Many manufacturers now provide SPF ratings for their garments, with SPF 20 being common, SPF 30-40 easy to find, and SPF50+ available with some searching.

In hot, dry environments, loose-fitting hooded base layers (often termed sun hoodies) offer excellent defense against the sun’s rays and its warming effects. Check fabric weight and design purpose to select the most suitable product. For instance, a skin-tight black base layer won’t help you feel cool in direct sunlight.


The feel of different fabrics is highly subjective. Some individuals may not find merino wool comfortable and rule it out entirely, while others might dislike polyester/polymer-based fabrics. Experimenting with different fabrics is crucial for success.

Ignoring thermal impacts, a close-fitting polyester base layer might feel more comfortable in a jungle and cause less chafing. Testing various layers and garments is key to finding the right fit.

Odour Resistance

Several fabrics possess anti-odour properties. Merino wool, for instance, is naturally anti-microbial but can absorb and hold a lot of moisture, which might work against its odour resistance.

Polymer-based fabrics can be treated with substances like POLYGEINE, impregnating them with anti-microbial chemicals that neutralize odours. This treatment is especially helpful for multi-day or high-exertion activities where sweat buildup is inevitable.

Unfortunately, no garment can entirely prevent body odour, but that’s part of the adventure.

Fabric Types

Consider the various fabric types available. However, fabric choice is subjective; some might prefer merino in the jungle, while others wouldn’t. Personal experimentation is crucial here.

Common fabrics and their properties include:

  • Merino: natural animal wool, anti-microbial, absorbent, good thermal properties but might feel coarse and dry slowly due to its hydrophilic and hydrophobic nature.
  • Bamboo (viscose/rayon): natural plant-based fabric, anti-microbial, absorbent, soft feel but dries slowly and might hold water rather than wick it away.
  • Synthetic (polyester, nylon, polypropylene, etc.): derived from petrochemicals, can be treated to resist odours, non-absorbent, soft feel, good thermal properties both wet and dry, highly adaptable but has a negative environmental impact due to production and microplastic pollution.

Choosing the Best

Determining the best base layer is challenging! Personal preference, environmental impact, comfort, and appearance all influence performance and perception.

In cold conditions, staying dry and warm is crucial. Avoid sweating, but if it occurs, ensure the garment wicks moisture away and dries quickly.

In hot conditions, you’ll rely on sweating and airflow for cooling. Choose a garment that maximizes heat transfer processes.

Ultimately, experience brings knowledge. If uncertain, ask questions, explore options, and experiment to find the most suitable choice.

→  Test out your new base layers on one of our Extreme Medicine Courses!

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