Long underwear, also known as base layers or thermal wear, is a must-have for anyone looking to stay warm and comfortable during the colder months. Whether you’re heading out for outdoor adventures like skiing or hiking, or simply trying to keep cozy during winter, the right long underwear can make all the difference. The best long underwear offers warmth, moisture-wicking capabilities, and a comfortable fit, ensuring you stay dry and warm in any condition. In this guide, we’ve reviewed the Best Long Underwear of 2025 to help you find the perfect pair for your needs.

What Makes the Best Long Underwear?

The best long underwear strikes a balance between warmth, comfort, and performance. Here are the features to look for:

• Fabric: Merino wool is a top choice for its natural insulation, moisture-wicking, and odor resistance. Synthetic blends are also great for affordability and durability.
• Fit: A snug fit ensures optimal warmth and prevents bulk under your outer layers.
• Versatility: The best long underwear can be used across various activities, from lounging to high-intensity outdoor sports.

Comparison Chart for the 7 Best Long Underwear

Best Long Underwear of 2025

1. Smartwool Men’s Classic Thermal Merino Base Layer Bottom

Best For: Cold-weather activities and layering.

Reasons to Buy:

• Excellent moisture-wicking properties.
• Slim fit allows unrestricted movement.
• Perfect for outdoor adventurers needing lightweight warmth.

Reasons to Avoid:

• Higher price compared to other options.

Short Review: The Smartwool Thermal Bottom offers premium comfort with its Merino wool fabric. Its slim fit is ideal for layering, making it a great choice for skiing, hiking, or any cold-weather activity.

2. Carhartt Men’s Force Midweight Synthetic-Wool Blend Base Layer Pant

Best For: Rugged outdoor activities.

Reasons to Buy:

• Durable poly-wool blend construction.
• Great odor resistance and sweat-wicking features.
• Affordable and rugged design.

Reasons to Avoid:

• Slightly less breathable than pure Merino wool.

Short Review: Carhartt’s midweight base layer pants are built for performance. They excel in regulating body temperature, especially during high-intensity activities.

3. MERIWOOL Men’s Base Layer 100% Merino Wool Thermal Pants

Best For: All-season outdoor enthusiasts.

Reasons to Buy:

• Superfine Merino wool ensures itch-free comfort.
• Lightweight but warm design perfect for layering.
• Quick-drying and easy to care for.

Reasons to Avoid:

• May lack stretch compared to synthetic options.

Short Review: The MERIWOOL thermal pants are a reliable and comfortable choice for camping, hiking, or lounging. They provide all-day warmth and comfort without overheating.

4. Merino Wool Base Layer Men’s Bottom Pants

Best For: Versatile layering and gift options.

Reasons to Buy:

• Available in lightweight, midweight, and heavyweight options.
• Comes with a pair of wool hiking socks.
• Comfortable and non-itchy design.

Reasons to Avoid:

• Higher price range for additional features.

Short Review: This Merino wool base layer is a versatile and thoughtful choice for winter sports or casual wear. The included wool socks add great value for outdoor enthusiasts.

5. 100% Merino Wool Bottoms Men’s Midweight Base Layer Pants

Best For: Extended outdoor use and cold weather.

Reasons to Buy:

• Midweight design suitable for fall, winter, and spring.
• Extremely soft and comfortable for all-day wear.
• Available in a wide range of sizes, including tall and plus sizes.

Reasons to Avoid:

• Slightly bulkier compared to lightweight options.

Short Review: Designed for versatility, these midweight Merino wool pants are perfect for layering during outdoor adventures. Their size inclusivity makes them accessible to everyone.

6. Smartwool Men’s Intraknit Thermal Merino Wool Base Layer 3/4 Bottom

Best For: High-intensity activities in cool weather.

Reasons to Buy:

• Blended Merino wool offers warmth and fast drying.
• Slim fit design enhances mobility.
• Built-in ventilation for moisture management.

Reasons to Avoid:

• Not ideal for extreme cold due to its 3/4 length.

Short Review: Smartwool’s Intraknit Thermal Base Layer is lightweight and breathable, making it a fantastic option for outdoor enthusiasts engaging in high-intensity activities.

7. Amazon Essentials Thermal Long Johns Underwear Set for Men

Best For: Budget-friendly winter wear.

Reasons to Buy:

• Affordable and accessible.
• Soft cotton-poly blend for lightweight warmth.
• Ideal for casual wear or layering.

Reasons to Avoid:

• Less moisture-wicking compared to Merino wool.

Short Review: Amazon Essentials offers a reliable and affordable option for staying warm during mild winters. Its breathable waffle-knit fabric is perfect for daily wear.

FAQs About the Best Long Underwear

1. What is the best material for long underwear?
   Merino wool is considered the best for its warmth, moisture-wicking, and odor resistance. Synthetic blends are great for durability.
2. Are all long underwear suitable for extreme cold?
   Not all. Look for midweight or heavyweight options for extreme cold.
3. How do I wash my long underwear?
   Most can be machine washed, but always check the care label for specific instructions.
4. What’s the difference between lightweight and midweight long underwear?
   Lightweight is better for mild temperatures, while midweight is ideal for colder conditions.
5. Can long underwear be worn alone?
   Yes, many long underwear options are designed for both layering and standalone use.
6. Does long underwear help with sweating?
   Yes, good long underwear wicks away sweat to keep you dry and warm.
7. Are there options for plus-size individuals?
   Yes, brands like Minus33 offer sizes up to 6XL.
8. How long does good long underwear last?
   High-quality options can last several years with proper care.
9. What’s the average cost of quality long underwear?
   Prices range from $40 to $150, depending on the material and brand.
10. Is long underwear itchy?
    No, high-quality Merino wool and synthetic options are designed to be soft and itch-free.

Final Thoughts

Choosing the Best Long Underwear of 2025 depends on your specific needs, whether it’s extreme cold weather or casual use. From Smartwool’s premium Merino wool designs to Carhartt’s rugged performance pants, there’s a perfect fit for everyone. Invest in the right base layer to stay warm, dry, and comfortable no matter the weather.