What Are Long Johns?

Summary

Long johns are a type of thermal underwear designed to be worn as a base layer beneath other clothing to provide warmth and help manage moisture. Modern long johns are typically made from materials such as wool or synthetic fabrics that can help wick moisture while providing insulation without excessive bulk. They are useful for winter sports, outdoor work, hiking, camping and everyday activities in cold weather. The right pair should fit comfortably close to the body and work effectively with the rest of your layering system.

Long johns are a familiar cold-weather staple, but today's versions are designed with much more advanced fabrics and construction than traditional thermal underwear. Understanding what long johns are and how they function can help you choose the right base layer for your next cold-weather adventure.

What Are Long Johns Used For?

Long johns are base-layer garments designed to provide warmth and help manage moisture in cold conditions.

The term "long johns" generally refers to long underwear that covers the arms and legs. Long john tops and bottoms are designed to sit close to the body so they can form the foundation of a cold-weather layering system. Iowa State University's Environmental Health and Safety guidance recommends moisture-wicking long underwear as the first layer for cold-weather exposure because it helps move perspiration away from the skin.[1]

Unlike ordinary shirts or pants, long johns are specifically designed to be worn beneath other garments. Their close-fitting construction helps minimize bulk while leaving room for additional insulating and protective layers.

Long johns can be useful for many cold-weather activities. Skiing, snowboarding, hiking, camping and outdoor work can all involve changing activity levels and temperatures, making a comfortable base layer an important part of the clothing system.

How Do Long Johns Keep You Warm?

Long johns help keep you warm by trapping heat close to your body while helping move moisture away from your skin.

A properly designed base layer helps create a layer of warmth next to the skin while allowing perspiration to move outward. Iowa State University explains that effective cold-weather layering uses fabrics that trap air warmed by the body while allowing moisture vapor from perspiration to move away from the skin.[1]

Moisture management is especially important when you're active in cold weather. Sweating can leave clothing damp and make you feel colder when activity slows down. Choosing a moisture-wicking long john can help you stay more comfortable as your activity level changes.

Long johns also work as part of a larger layering system. A base layer manages moisture, an insulating layer adds warmth and an outer layer helps protect against wind and precipitation.

When choosing long johns, consider these features:

• Moisture management: Helps move perspiration away from your skin

• Insulation: Adds warmth without excessive bulk

• Breathability: Allows excess heat and moisture to escape

• Stretch: Supports comfortable movement during activity

• Low bulk: Makes it easier to add additional layers

What Materials Are Used for Long Johns?

Long johns are commonly made from wool, synthetic fabrics or blends designed for cold-weather performance.

Wool can provide warmth while also helping manage moisture. Synthetic fabrics such as polyester and polypropylene are popular for their durability and quick-drying properties. Iowa State University notes that synthetic fibers can move perspiration vapor away from the skin while wool can provide insulation and ventilation.[1]

The best material depends on your activity, weather conditions and personal preferences. If you're participating in high-output activities such as skiing or hiking, you may prioritize breathability and moisture management. For less active time outdoors, you may prefer a warmer fabric or heavier construction.

When comparing long john materials, consider the following:

• Wool: Warm, breathable and effective across changing conditions

• Synthetic fabrics: Lightweight, durable and quick drying

• Wool blends: Combine wool with other fibers for added durability

• Lightweight fabrics: Useful for active pursuits or moderate temperatures

• Heavier fabrics: Better suited to colder conditions or lower activity levels

When Should You Wear Long Johns?

Long johns are most useful when cold temperatures or extended outdoor exposure make additional insulation necessary.

Winter activities such as skiing, snowboarding, snowshoeing and winter hiking can benefit from a quality base layer. Long johns are also useful for camping, hunting and outdoor work where you'll spend extended periods outside.

The weight of your long johns should match the conditions and your activity level. Lightweight options can work well when you're moving frequently while heavier thermal options can provide additional insulation when temperatures are particularly cold or you're likely to remain inactive for longer periods.

Long johns can also be useful for everyday winter activities. Wearing them beneath regular pants or other clothing can provide additional warmth while allowing you to avoid relying on one bulky outer garment.

If you'd like to learn more about long johns, base layers and cold-weather layering, refer to our resources pages for additional information and helpful guides.

FAQ

1. Are long johns the same as thermal underwear? Yes. Long johns and thermal underwear are commonly used to describe base-layer garments designed to provide warmth and help manage moisture.

2. Should long johns fit tightly? Long johns should fit close to the body without restricting movement. A comfortable fit allows them to function effectively as a base layer.

3. Can you wear long johns in warm weather? Lightweight base layers can be useful in mild conditions when moisture management is important. Heavier thermal long johns are generally better suited to cold weather.

4. Are wool or synthetic long johns better? Both materials can perform well. Wool offers warmth and breathability while synthetic fabrics are known for durability and quick drying. Your choice should depend on your activity and the conditions you expect.

5. Do long johns go under or over underwear? Long johns are generally worn as a base layer beneath your outer clothing. Whether they go over traditional underwear depends on the garment design and your personal preference.

Citations

1. Winter Weather, Environmental Health and Safety, Iowa State University, Accessed August 21, 2026, https://www.ehs.iastate.edu/winter-weather