A Practical Guide to Materials, Colors, and NIR Penetration
Part 5 of the series: Light on Healing: How Red Light and Sunlight Protect Your Aging Brain
- Part 1: Melatonin: Not Just a Sleep Hormone – The Mitochondrial Antioxidant You’ve Never Heard Of
- Part 2: The Surprising Secret of Blue Zones: Daily Sunlight Heals
- Part 3: What Is Photobiomodulation? Red Light, NIR, and the Skin-Brain Axis
- Part 4: Does Hair Block Near-Infrared Light? A Practical Guide
🎧 ▶️ Press the play button below to listen.
Introduction
In the previous article, we explored how hair can absorb and scatter near-infrared (NIR) light.
But here is an even bigger question for anyone who spends time outdoors or uses NIR therapy at home:
What if I am wearing a hat? Or a shirt? Or a jacket?
Does a baseball cap block NIR? What about a winter beanie? A cotton t-shirt? A polyester gym shirt? A thick wool sweater?
And what about color — does a black shirt block more NIR than a white one? Does red clothing make a difference?
This article answers those questions so you can make informed choices about what you wear when you want NIR to reach your skin — and when you want to block it.
Let us start with the short answer.
The Short Answer
Yes, most hats and clothing block the majority of NIR light.
- Thick, opaque materials (denim, wool, leather, thick cotton, fleece) block nearly all NIR.
- Thin, loosely woven materials (thin cotton, linen, mesh, some athletic fabrics) allow some NIR to pass through — but still reduce it significantly.
- Color matters, but less than thickness and weave. Dark colors absorb more NIR; light colors reflect more. A thick white shirt still blocks most NIR.
- Multiple-layer blocks more than single-layer blocks. Two thin shirts block more than one.
- Wet clothing may transmit slightly more NIR than dry, but not enough to rely on.
If your goal is to get NIR to your skin (for brain health, mitochondrial melatonin, or systemic effects), bare skin is always best. But if you need to wear clothing (for sun protection, warmth, modesty, or social reasons), you can make choices that minimize NIR loss.
How Materials Affect NIR Transmission
Different materials have different optical properties. Here is how common clothing materials perform:
| Material | Typical Thickness | NIR Transmission | Notes |
|---|---|---|---|
| Thin cotton (t-shirt weight) | 0.3–0.5 mm | 10–30% | Some NIR gets through, but most is blocked |
| Thick cotton (denim, canvas, sweatshirt) | 1–2 mm | <5% | Nearly complete blockage |
| Polyester / athletic fabric (thin) | 0.2–0.5 mm | 15–40% | Better than cotton at same thickness |
| Polyester / fleece (thick) | 2–5 mm | <1% | Almost total blockage |
| Wool (sweater, beanie) | 2–5 mm | <1% | Complete blockage |
| Linen (loose weave, thin) | 0.3–0.6 mm | 20–40% | Better than tight weave; light passes through gaps |
| Nylon / spandex (athletic, thin) | 0.2–0.4 mm | 15–35% | Similar to polyester |
| Silk (thin) | 0.1–0.3 mm | 25–50% | One of the best for NIR transmission among fabrics |
| Mesh / fishnet | 1–2 mm (gaps) | 50–80% (through gaps only) | NIR passes through holes, not material itself |
| Leather | 1–2 mm | <1% | Complete blockage |
| Bare skin (no clothing) | N/A | ~90–95% | Optimal (some reflection occurs) |
Key takeaway: No common clothing material is truly “transparent” to NIR. The best you can hope for with thin, light-colored, loosely woven fabrics is partial transmission (10–50%). Most everyday clothing blocks 70–95% of NIR.
Does Color Matter?
Yes, but less than most people think.
How Color Affects NIR
- Dark colors (black, navy, dark brown, dark green, dark purple) absorb more light across all wavelengths, including NIR. A black shirt will absorb NIR and convert it to heat (which you may feel as warmth).
- Light colors (white, beige, light gray, pastels) reflect more visible light and some NIR. A white shirt reflects more NIR away from your skin — meaning less reaches you, not more.
- Bright colors (red, orange, yellow, bright blue) fall somewhere in between. Red is particularly interesting (see below).
The Red Clothing Question
You might wonder: If red light therapy uses red wavelengths, does wearing red clothing help?
No. Wearing red clothing does not enhance NIR or red light delivery. Here is why:
- Red clothing reflects red light (that is why it looks red to your eyes). Reflection means the light bounces off, not through.
- The red light used in therapy (660 nm) is a specific narrow band. Red dye in clothing absorbs some of that band and reflects the rest.
- Even a thin red shirt will block most of the red and NIR light, similar to any other colored shirt of the same thickness and weave.
Key takeaway: For NIR transmission, thickness and weave matter more than color. A thin white shirt and a thin black shirt will have similar NIR transmission (both poor). A thin red shirt is no better.
Does Color Affect Heat Absorption?
Yes, but that is different from NIR transmission.
- Black clothing absorbs more NIR and converts it to heat. You will feel warmer in black clothing on a sunny day — because the NIR is being absorbed by the fabric, not transmitted to your skin.
- White clothing reflects more NIR, so the fabric stays cooler. But the reflected NIR never reaches your skin.
Practical advice for sunny days: If you want NIR to reach your skin, wear as little clothing as possible (or very thin, loose-weave, light-colored fabric). If you want to stay cool, wear white or light-colored clothing — but accept that NIR is being reflected away.
How Many Layers? Thickness and Weave Matter
The single most important factor for NIR penetration is the amount of material the light has to pass through.
Single Layer vs. Multiple Layers
- One thin cotton shirt: 10–30% NIR transmission
- Two thin cotton shirts (layered): 1–9% transmission (layers multiply the blocking effect)
- One thick sweatshirt: <5% transmission
- One thin shirt + one jacket: <1% transmission
Key takeaway: Layering is extremely effective at blocking NIR. If you are wearing multiple layers for warmth or sun protection, assume that zero NIR reaches your skin.
Weave Density
Even with the same material and thickness, weave matters.
- Tight weave (dress shirt, denim, canvas): Low NIR transmission (light cannot easily pass through gaps)
- Loose weave (linen, mesh, open-knit sweater): Higher NIR transmission (light passes through gaps between fibers)
Practical advice: If you must wear clothing and want NIR to reach your skin, choose loose weaves over tight weaves, and thin materials over thick ones.
Does Wet Clothing Allow More NIR Through?
This is a common question for swimmers, runners, or anyone caught in the rain.
The short answer: Wet clothing may transmit slightly more NIR than dry clothing, but not enough to rely on.
- Water has a refractive index closer to skin than air does. When fabric is wet, the optical mismatch between air and fabric is reduced, which can reduce scattering.
- However, wet fabric also tends to cling to skin, eliminating air gaps that might otherwise allow some light to pass around fibers.
- Most studies on wet fabric focus on UV protection, not NIR. For UV, wet fabric often provides less protection (more transmission). For NIR, the effect is likely similar but small.
Practical advice: Do not rely on wet clothing for NIR exposure. If you want NIR, remove the clothing or wear minimal, thin, loose-weave fabrics.
Practical Scenarios: What Should You Wear?
| Scenario | Goal | Recommendation |
|---|---|---|
| Home NIR therapy session (panel device) | Maximum NIR to skin | Wear nothing over the area being treated. Bare skin is best. |
| Morning sunlight exposure (low UV) | Natural NIR for brain/body | Wear minimal clothing (shorts, tank top, swimsuit). Expose as much skin as possible. |
| Midday sun (high UV) | Avoid sunburn while getting some NIR | Wear UV-protective clothing on high-risk areas (face, shoulders). Expose lower legs or arms briefly. Accept that clothing blocks NIR. |
| Cool weather (fall/spring) | Comfort + some NIR | Wear one thin, light-colored, loose-weave layer (linen, thin cotton). Add 20–30% more sun exposure time. |
| Cold weather (winter) | Warmth | Accept that winter clothing blocks nearly all NIR. Use artificial NIR devices indoors instead. |
| Outdoor exercise (running, cycling) | Performance + NIR | Wear minimal clothing (shorts, sports bra, tank top). Choose light colors for heat reflection. Remove outer layers when possible. |
| Swimming / beach | Sun protection + NIR | Wear minimal swimwear. Use sunscreen on exposed skin. Do not rely on wet clothing for NIR. |
| Modesty / cultural dress | Respect practice + some NIR | Choose thin, light-colored, loose-weave fabrics (linen, thin cotton, silk). Accept partial benefit. |
What About Hats?
Hats deserve their own section because the head is a key target for brain health NIR.
| Hat Type | Material | Typical NIR Transmission | Best Use Case |
|---|---|---|---|
| No hat | Bare skin | 90–95% | Optimal for NIR therapy |
| Thin cotton beanie | Cotton (0.5 mm) | 10–20% | Minimal benefit; remove if possible |
| Baseball cap (front) | Thick cotton/polyester | <5% | Near-total blockage |
| Mesh trucker hat (mesh) | Plastic mesh | 50–80% (through holes) | Acceptable if holes align with scalp |
| Wide-brim straw hat | Straw with gaps | 20–40% (through gaps) | Decent for outdoor NIR |
| Winter wool beanie | Wool (3–5 mm) | <1% | Complete blockage |
| Thin scarf / wrap (hijab, turban) | Cotton or silk (0.3 mm) | 10–30% | Partial benefit; better than nothing |
| Leather cap | Leather | <1% | Complete blockage |
| UV-protection sun hat | Specialized fabric | <5% (intentionally blocks) | Best for UV protection, not NIR |
Key takeaway: No hat is best. If you must wear a hat, choose thin, light-colored, loosely woven fabrics, or hats with mesh/straw gaps.
What About Sunscreen on Skin Under Clothing?
This is another common question.
Sunscreen is designed to block UV, not NIR. Most sunscreens allow NIR to pass through.
- Mineral sunscreens (zinc oxide, titanium dioxide) reflect UV and some visible light, but they are largely transparent to NIR.
- Chemical sunscreens absorb UV and are also largely transparent to NIR.
Practical advice: If you are wearing clothing that blocks NIR, adding sunscreen underneath does not help (the clothing is already blocking). If you are exposing bare skin for NIR, sunscreen will not block NIR — so you can protect against UV while still getting NIR benefits.
Summary Table: Clothing and NIR Transmission
| Clothing Type | Typical NIR Transmission | Best Use Case |
|---|---|---|
| Bare skin | 90–95% | Optimal for NIR therapy |
| Thin silk blouse/shirt | 25–50% | Good for modesty + partial NIR |
| Thin linen shirt (loose weave) | 20–40% | Good for warm weather + partial NIR |
| Thin cotton t-shirt | 10–30% | Acceptable for partial NIR |
| Thin polyester athletic shirt | 15–40% | Acceptable for exercise + partial NIR |
| Thick cotton sweatshirt | <5% | Blocks nearly all NIR |
| Denim jacket / jeans | <5% | Blocks nearly all NIR |
| Wool sweater | <1% | Complete blockage |
| Leather jacket | <1% | Complete blockage |
| Multiple layers (any material) | <1–9% | Assume zero NIR reaches skin |
Conclusion
Hats and clothing block most near-infrared light.
- Thick, opaque, or dark-colored fabrics block nearly all NIR (95–99%).
- Thin, light-colored, loosely woven fabrics allow some NIR to pass (10–50%).
- Multiple-layer blocks are more than single-layer blocks.
- Color matters less than thickness and weave. Red clothing does not enhance NIR delivery.
- Bare skin is always best for NIR delivery to your skin and brain.
But life is not always optimal. If you must wear clothing for sun protection, warmth, modesty, or social reasons, you can still get partial NIR benefits by choosing thin, light, loose fabrics — or by exposing small areas of bare skin (arms, lower legs, neck, face).
And remember: sunscreen does not block NIR. Clothing does. Choose accordingly.
Takeaway Messages
- Most hats and clothing block 70–95% of NIR light — often more.
- Thickness and weave matter more than color. A thick white shirt blocks almost as much as a thick black shirt.
- Thin, loosely woven, light-colored fabrics (linen, thin cotton, silk) allow 10–50% of NIR to pass through.
- Mesh, straw, and ventilated hats allow NIR through the gaps — position the gaps over your scalp.
- Multiple layers block NIR very effectively. Assume zero NIR reaches skin through two layers.
- Red clothing does not help. It reflects red light, blocking it from reaching your skin.
- Wet clothing may transmit slightly more NIR, but not enough to rely on.
- Bare skin is always best for NIR therapy and outdoor NIR exposure.
- Sunscreen does not block NIR — but a hat or shirt does.
- If you cannot remove clothing, expose small areas of bare skin (arms, lower legs, neck, face) for partial benefit.
- In cold weather, use artificial NIR devices indoors. Winter clothing blocks nearly all NIR.
Don’t Get Sick!
About Dr. Jesse Santiano, MD
Dr. Santiano is a retired internist and emergency physician with extensive clinical experience in metabolic health, cardiovascular prevention, and lifestyle medicine. He reviews all medical content on this site to ensure accuracy, clarity, and safe application for readers. This article is for educational purposes and is not a substitute for personal medical care.
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Related:
References:
- Khorshid, M., Ma, J., & Unwin Teji, J. (2025). The transmission of near-infrared electromagnetic radiation through different fabric types. In CIE Midterm Meeting Proceedings. Vienna, Austria: International Commission on Illumination. https://discovery.ucl.ac.uk/id/eprint/10213150/
- Kuwabara, K., Kubota, H., Hamada, Y., & Nakamura, M. (2013). Study on evaluation method of spectral reflectance and transmittance of clothing in the visible and near infrared ranges. Descente Sports Science, 34. https://www.shinshu-u.ac.jp/faculty/textiles/db/seeds/pages/71157/en.php
- Wilhelm, R. H., & Smith, J. B. (1949). Transmittance, reflectance, and absorptance of near infrared radiation in textile materials. Textile Research Journal, 19(2), 73-88. https://doi.org/10.1177/004051754901900202
Disclaimer:
This article is for educational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician before making health decisions based on the TyG Index or other biomarkers.
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