Top 7 Sweat-Absorbing Materials for Undershirts Comparison

Sweaty underarms, damp chests, and visible sweat stains—we’ve all been there. The solution? Choosing an undershirt with the right sweat-absorbing material. But with so many options (cotton, Modal™, Merino wool, and more), how do you know which one performs best? We’re breaking down the top 7 sweat-absorbing materials for undershirts, comparing their pros, cons, and ideal use cases to help you find your perfect match.

First, a quick reminder: no single material is “best” for all situations. Sweat behavior varies (light vs. heavy perspiration, hot vs. cool climates), so the most effective undershirts often combine multiple materials into a “fabric system.” But understanding each material’s strengths and weaknesses is key to choosing wisely.

In this guide, we break down the most effective sweat-absorbing materials for undershirts, explaining how each fabric performs, when it works best, and where it falls short—so you can choose the right option for your climate, lifestyle, and wardrobe.

• Cotton (Including Pima Cotton)
• Modal™
• Lycra® (Spandex)
• Merino Wool
• Mesh (Synthetic or Natural Blends)
• Moisture-Wicking Synthetics (Polyester, Polyamide, Polyurethane)
• Fabric Systems: The Most Effective Sweat Solution
• Side-by-Side Comparison Chart
• Final Thoughts on Sweat-Absorbing Undershirt Materials
• FAQs

1. Cotton (Including Pima Cotton)

How it performs for sweat:

Cotton is a natural fiber beloved for its softness and breathability and it’s great at absorbing sweat, which feels comfortable against the skin during light sweating or short wear. However, cotton’s biggest flaw is that it holds onto moisture once wet. Wet cotton dries slowly, leading to prolonged dampness, heaviness, and friction (not ideal for high-sweat areas or all-day wear).

Pima Cotton Upgrade:

Pima cotton (with longer fibers) offers superior softness, durability, and absorbency compared to regular cotton. It’s not ideal for full-garment construction (since it still holds moisture), but it shines as a targeted solution like in permanent underarm sweat shields, where its absorption power traps moisture at the source.

Best for:

Light sweaters, short outings, or as a sweat-shield material (not full undershirts). Great for those who prioritize natural softness over all-day sweat management.

2. Modal™

How it performs for sweat:

Modal™ is a plant-based fiber made from sustainably sourced beechwood pulp. Its ultra-fine fibers create a smooth, lightweight fabric that feels soft against the skin while allowing air to circulate—especially where you need it most. Unlike traditional cotton, Modal helps regulate moisture by absorbing sweat gradually and releasing it efficiently, so you feel fresh, not damp, throughout the day.

Bonus perks:

Modal maintains its softness and shape from morning to night. It resists stiffness, heaviness, and that “worn-out” feeling, even after hours of wear under fitted or structured clothing. Think of consistent comfort, no matter how long your day runs.

Best for:

All-day wear, hot climates, or under structured/fitted clothing. Pair it with targeted underarm protection for maximum sweat control.

3. Lycra® (Spandex)

How it performs for sweat:

Lycra® (a synthetic stretch fiber) doesn’t absorb sweat on its own—but it’s a critical partner for sweat management. Fabrics without stretch gap or shift away from the body, allowing sweat to pool and spread before absorption. Lycra® keeps undershirts close to the skin (without compression), moving with you to maintain coverage in sweat-prone areas.

Common use case:

Lycra® is almost always blended (e.g., 90% Modal™ + 10% Lycra®) to add four-way stretch, shape recovery, and lasting fit—key for ensuring other sweat-absorbing materials perform their best.

Best for:

Any undershirt (as a blend component). Essential for active lifestyles or anyone who hates ill-fitting, bunching undershirts.

Numi’s Modal undershirts are made with 90% thermo-regulating Modal™ and 10% LYCRA®, creating a four-way stretch fabric that offers freedom of movement, shape recovery, and lasting comfort. The fabric is shrink-resistant and fade-proof, designed for long-term wear, and engineered to work seamlessly with Numi’s built-in underarm sweat shields.

4. Merino Wool

How It Performs for Sweat:

Merino wool manages sweat differently than most fabrics. Instead of trapping moisture on the skin, it absorbs moisture vapor and releases it gradually, helping underarms feel drier without that cold or clammy sensation. Its natural odor resistance prevents odor-causing bacteria from building up, so you stay feeling fresh—even with extended wear.

Best For:

• Cooler climates and transitional seasons
• Long days, travel, and fluctuating indoor–outdoor temperatures
• Women who want sweat and odor control without synthetic fabrics

Why Women Love It:

Merino wool naturally regulates body temperature—keeping you warm when it’s cold and cool when it’s not. Lightweight merino base layers are especially well-suited for workwear and everyday layering, offering comfort, breathability, and confidence without bulk.

5. Mesh (Synthetic or Natural Blends)

How it performs for sweat:

Mesh is a lightweight, open-structure fabric designed for maximum airflow—it feels ultra-cool against the skin and reduces heat buildup (perfect for hot weather). However, mesh prioritizes breathability over absorption: its open pores let sweat pass directly through, so it doesn’t stop visible sweat on its own.

Best use case:

Mesh works best when combined with built-in underarm sweat shields, allowing airflow without sacrificing protection. It’s not ideal as a standalone undershirt for heavy sweaters.

Best for:

Hot climates, layering under loose clothing, or as a panel (not full garment) in undershirts. Great for those who prioritize coolness over full sweat blockage.

6. Moisture-Wicking Synthetics (Polyester, Polyamide)

How it performs for sweat:

Synthetics like polyester or polyamide are engineered for moisture-wicking: they pull sweat away from the skin and spread it across the fabric to evaporate quickly. This works well for activewear (where rapid drying is key), but there’s a catch for everyday undershirts: they spread sweat to sleeves, seams, or outer layers—increasing visible sweat marks.

Polyurethane (PU) is sometimes added to synthetic fabrics as a thin barrier or coating designed to block moisture from passing through. While this can prevent sweat from reaching outer layers, it also limits airflow—often trapping heat and creating a clammy feel over time.

Considerations:

Some synthetic blends can feel “plasticky” against the skin, and they’re not as breathable as natural fibers like Modal™ or Merino. They also lack natural odor resistance (though some are treated with anti-odor coatings).

Best for:

Workouts or high-intensity activities (not everyday wear under dress clothes). Great for those who need rapid drying during physical activity.

7. Fabric Systems (Blends + Targeted Materials)

How it performs for sweat:

While not a single material, fabric systems are the most effective solution for sweat control. They combine complementary materials to address all sweat-related issues: a breathable base (Modal™ or Merino) for temperature regulation, stretch (Lycra®) for fit, and targeted absorption (Pima cotton sweat shields) for high-sweat areas.

Example (Numi Undershirts):

90% thermo-regulating Modal™ (base layer for breathability), 10% Lycra® (stretch and fit), and permanent Pima cotton underarm sweat shields (targeted absorption). This system blocks sweat transfer, stays breathable, and feels invisible under clothes—no single material could do all three.

Best for:

Anyone seeking all-day sweat protection, comfort, and versatility. Ideal for office wear, special occasions, or daily use where confidence matters.

Side-by-Side Comparison Chart

Final Thoughts on Sweat-Absorbing Undershirt Materials

For everyday wear and maximum sweat control, fabric systems (like Modal™ + Lycra® + Pima cotton) are the clear winner—they combine the strengths of individual materials to address absorption, breathability, fit, and odor control.

If you’re choosing a single-material undershirt: opt for Modal™ for hot weather/all-day comfort, Merino wool for cool climates/odor control, or Pima cotton for targeted sweat absorption (e.g., sweat shields).

Remember: the best material for you depends on your lifestyle. Whether you’re a light sweater, a heavy sweater, or someone who commutes between hot and cold environments, there’s a sweat-absorbing undershirt material (or blend) that will keep you comfortable and confident.

Now that you know how undershirt materials perform, you can start browsing Numi sweat-proof undershirts designed for your needs—or dive deeper into styling with our What to Wear Under Guide to find the right layer for every outfit.

FAQs

What is the best fabric for undershirts?

The best fabric for undershirts depends on how and where you wear them. For all-day comfort and reliable sweat control, breathable fabrics that manage moisture—rather than just absorbing it—perform best. Modal™ is ideal for everyday wear and warm climates, Merino wool works well for cooler or transitional conditions, and fabric systems that combine multiple materials offer the most balanced performance overall.

Which fabric is best for ladies?

The best undershirt fabrics for women are those that feel soft against the skin, layer smoothly under clothing, and help manage sweat discreetly. Lightweight, breathable materials like Modal™ and fine Merino wool are especially popular because they regulate moisture without bulk. For added confidence, undershirts with targeted underarm absorption can help prevent visible sweat under fitted or light-colored clothing.

What fabric is best for sweating?

The best fabrics for sweating are those that balance breathability with moisture management. While cotton absorbs sweat, it can hold moisture and feel heavy over time. Modal™ helps regulate moisture so fabric stays drier longer, and Merino wool manages sweat vapor while resisting odor. For maximum sweat control—especially under the arms—fabric systems that combine breathable base layers with targeted absorption are the most effective.

What fabric does not show armpit sweat?

Fabrics that absorb moisture and prevent it from spreading are the least likely to show armpit sweat. Soft, breathable base layers paired with targeted underarm absorption (such as built-in sweat shields) are far more effective than relying on outer fabrics alone, especially under fitted or light-colored clothing.

What fabrics should you avoid in hot weather?

In hot weather, fabrics that trap heat or show moisture easily such as heavy synthetics, satin, silk, and tightly woven polyester can make sweating feel worse and more visible. These materials limit airflow or highlight moisture, which is why breathable fabrics and smart layering underneath matter more than the outer fabric alone.

What is the coolest material for undershirts?

The coolest materials for undershirts are lightweight, breathable fabrics that regulate moisture instead of trapping it, such as Modal™ or fine Merino wool. These fabrics allow airflow and release moisture gradually, keeping the body feeling cooler and more comfortable than heavy cotton or synthetic performance fabrics worn under regular clothing.