Why "Cotton Kills" in the Outdoors (And What to Wear Instead)

You have probably heard the phrase among experienced hikers and survival experts: "Cotton Kills."

It sounds dramatic. But in the wilderness, your favorite cotton t-shirt and blue jeans are actually dangerous. In fact, wearing them in cold or wet weather is the #1 cause of hypothermia for hikers.

But why? What makes this soft, comfortable fabric so deadly outdoors?

⚠️ The Golden Rule: Never wear cotton socks, cotton t-shirts, or denim jeans if you are going further than 1 mile from your car.

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1. The Sponge Effect 🧽

Cotton is hydrophilic, which means it loves water. It can absorb up to 27 times its weight in water.

When you hike, you sweat. Even in winter. Cotton absorbs that sweat and holds it directly against your skin. Unlike wool or polyester, cotton refuses to let the moisture go.

nce cotton is wet, it loses 95% of its insulating ability. It stops being a sweater and starts being a refrigerator.

2. The Chilling Truth (Hypothermia)

Here is the scary math: Water conducts heat away from your body 25 times faster than air.

If you are wearing a wet cotton shirt and a cold wind blows, your body temperature will drop rapidly. This is called "evaporative cooling." It’s great in the summer heat, but in the mountains, it can lead to hypothermia even in 50°F (10°C) weather.

3. What Should You Wear Instead?

You need fabrics that are hydrophobic (water-hating) or wicking. Here are the two best options:

A. Merino Wool 🐑

The gold standard. It pulls moisture away from your skin and—this is magic—it keeps you warm even when it is soaking wet.

B. Synthetics (Polyester/Nylon) 🧪

Cheap, durable, and dries incredibly fast. Most athletic shirts (like Nike Dri-Fit) are made of this.

Pro Tip for Feet: Never hike in cotton socks! They cause friction when wet, which leads to painful blisters. Read our comparison of Boots vs. Trail Runners to see what pairs best with wool socks.

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Summary

Save your cotton hoodies and jeans for the campfire or the city. On the trail, stick to wool or synthetics. It’s not just about comfort; it’s about safety.

Want to master your clothing setup? Read our full guide on The 3-Layer System to stay warm in any weather.