Learn about Base Layers and Underwear

Base Layer
Underpants

Base Layer

Although base layers provide some insulation, their main purpose is to wick moisture away from your skin to prevent cooling by evaporation. Insulation is mostly the job of your mid and outer layers, not your base layer. Your base layer should fit closely and contact as much skin as possible to allow maximum wicking. It shouldn’t be so tight that it’s restrictive.

Base layers typically come in 3 weights (thicknesses)—light, mid, and heavy. Heavy-weight base layers are more insulative but dry more slowly and wick less efficiently. For these reasons, it’s best to avoid them.

Base-layer Bottoms

Also called long underwear, thermal underwear, or long johns, these usually aren’t necessary while you’re hiking unless it’s very cold. However, they may be necessary when you are resting in moderately cold weather. They’re also great for sleeping in cold weather.

Base-layer Top

A base-layer top is essential in cold or cool weather. In warm or hot weather, you can wear a base-layer top with nothing over it.

Base-layer Materials

Recommended materials for base layers:

Synthetic (polyester and/or nylon)
Merino or Alpaca wool

Synthetic vs Merino Wool

	Pros	Cons	Other considerations

	Pros	Cons	Other considerations
Synthetic	More affordable More durable Absorbs less moisture Moisture evaporates more quickly Dries more quickly Can be slightly more breathable	Less insulative (but insulation is not the purpose of the base layer) Retains body odor
Merino Wool	More insulative (but insulation is not the purpose of the base layer) Resists body odor	More expensive Less durable Absorbs more moisture Moisture evaporates more slowly Dries more slowly Can be slightly less breathable	Warmer when wet (can be a pro or a con)

Other Materials

Cotton

Cotton is terrible for base layers. It absorbs water and dries very slowly.

Silk

Silk isn’t durable, doesn’t resist body odor, and doesn’t wick as well as synthetics or merino wool.

Bamboo

Bamboo base layers are expensive and don’t dry as quickly as synthetics or merino wool.

Hemp

Hemp is expensive and not very warm or water resistant.

Underpants

Underpants are more important than you might think. They should be made of breathable, stretchable synthetic materials such as polyester and spandex.

It’s crucial that your underpants don’t chafe. I was once forced to take a 3-day break from a 9-day backpacking trip to recover from chafing caused by unsuitable underpants. Avoid cotton or cotton blends as they absorb sweat, causing chafing. To prevent chafing for men, I recommend Hanes Total Support Pouch Boxer Briefs or equivalent. You can also apply Body Glide. If you are prone to chafing, you might want to pack a tube of zinc oxide ointment.