The Science: Why Dark Shirts Get Hotter

It comes down to how different colors interact with sunlight. Sunlight is made up of a mix of wavelengths—visible light, ultraviolet, and infrared. When light hits a piece of fabric, one of two things happens: it either gets reflected back or gets absorbed and converted into heat.

Dark colors absorb most of the light that hits them across the visible spectrum. Black, in particular, absorbs nearly all wavelengths without reflecting any back—that’s literally why we see it as black. All that absorbed light energy turns into heat, and that heat transfers to the fabric surface and then to your body.

Light colors do the opposite. White reflects nearly all visible wavelengths, which is why we perceive it as white. Less absorbed light means less heat generated in the fabric, which means a cooler shirt on your skin.

The Data: 9 Colors Ranked by Heat Absorption

In 2019, researcher Toshiaki Ichinose from Japan’s National Institute for Environmental Studies conducted a controlled outdoor experiment to find out exactly which shirt colors run hottest. His team placed nine same-material polo shirts side by side in direct summer sunlight and used a thermographic camera to measure each shirt’s surface temperature after five minutes of exposure.

The results were clear. Here’s the full ranking, coolest to hottest:

The Surprise: Dark Green Is Actually Worse Than Black

Most people assume black is the worst color to wear in the sun. The Ichinose study confirmed that’s true for visible light—but when the team expanded their analysis to include near-infrared radiation (the invisible portion of sunlight that carries a huge amount of heat energy), something unexpected showed up.

Dark green absorbed 87% of infrared radiation. Black absorbed 86%. White absorbed only 63%.

So if you’re ordering crew shirts in dark green thinking it’s a safer bet than black, it’s actually slightly worse when you factor in the full spectrum of solar radiation. Both dark green and black shirts topped out at over 45°C (113°F) on their surfaces during the test—more than 50% hotter than the white shirts.

Real-World Proof: The NWS Experiment

The Japanese study isn’t the only one. In August 2023, during a heat wave that brought record temperatures to the Midwest, the National Weather Service station in Kansas City ran their own experiment. They laid out a variety of jerseys and t-shirts in the afternoon sun and measured their surface temperatures.

The results backed up the science perfectly. The black and maroon shirts hit surface temperatures in excess of 150°F. The white t-shirt and white jersey stayed significantly cooler than everything else. The NWS summed it up simply: “Clearly the darker colored shirts got a lot warmer in the afternoon sun.”

A similar test by a local TV meteorologist found that a dark gray shirt reached 150°F within one hour of being in direct sunlight—a 70°F difference from when it started. That gray shirt hit over 130°F in just five minutes.

Why This Matters for Outdoor Workers

This isn’t just about comfort. For landscapers, construction crews, roofers, and anyone else working outside in the Sun Belt, heat is one of the most serious occupational hazards on the job.

The numbers are sobering. According to OSHA, from 2017 through 2022, there were 211 heat-related fatalities reported through workplace inspections nationwide. Construction and landscaping were consistently among the industries with the highest numbers of both hospitalizations and fatalities. The Bureau of Labor Statistics reported an average of 40 heat-related worker deaths per year between 2011 and 2022, with an estimated 3,389 heat injuries per year resulting in days away from work—and those numbers are widely considered to be significant underestimates.

OSHA also notes that 50% to 70% of outdoor heat fatalities occur in the first few days of working in hot conditions, before the body has had a chance to build heat tolerance. And the CDC specifically recommends that construction workers wear light-colored, loose-fitting, breathable clothing as one of the baseline steps for heat illness prevention.

The clothing you choose for your crew isn’t the only factor in heat safety—hydration, rest breaks, and shade matter just as much. But it is one of the easiest factors to control. And when you’re ordering custom shirts for your team anyway, choosing the right color costs nothing extra.

Arizona: The Toughest Test on Earth

If you’re based in Arizona, you already know this isn’t a hypothetical. We’re based in Maricopa, Arizona, and we watch outdoor workers battle the heat every single summer. In 2024—the hottest year on record globally—Phoenix hit 100°F or higher for 113 consecutive days, shattering the previous record of 76 days set in 1993. The area saw nearly 70 days above 110°F.

Maricopa County reported over 600 heat-related deaths in 2023—a 52% increase from 2022—and 2024 numbers tracked similarly high. Outdoor workers, including construction crews and landscapers, are among the most vulnerable. A San Francisco Fed analysis found that frontline outdoor workers make up roughly 20% of the Phoenix workforce, and the average Maricopa County outdoor worker could lose approximately $5,000 in earnings per year and 41 days of work due to extreme heat by 2065.

Arizona has no state heat standard written into law, though cities like Phoenix, Tempe, and Tucson have enacted local workplace heat ordinances requiring employers to provide water, rest, shade, and acclimatization plans. OSHA proposed a federal heat standard in August 2024, but it remains under review.

Fabric Matters Too: Cotton vs. Polyester vs. Blends

Color is the biggest factor in solar heat absorption, but fabric type controls what happens to the heat once it’s there. For outdoor work shirts, you’re basically choosing between three main options:

100% Cotton

How it works: Cotton is naturally breathable and allows air to circulate through the weave. It absorbs sweat and holds it in the fabric, where it can evaporate and cool you down through evaporative cooling.

The trade-off: Once cotton gets soaked with sweat, it stays wet. In high humidity, this makes it heavy, clingy, and slow to dry. In dry heat like Arizona, though, it actually works pretty well because the low humidity lets the moisture evaporate quickly.

100% Polyester

How it works: Polyester is hydrophobic—it doesn’t absorb moisture. Instead, it pulls sweat to the outer surface of the fabric where it evaporates fast. It dries quickly and is extremely durable.

The trade-off: Unblended polyester can trap heat and feel stuffy against the skin. It also tends to hold onto odors. It works best when it’s been engineered with moisture-wicking technology built into the weave.

Cotton-Polyester Blends (the sweet spot)

How it works: A blend—typically around 60–65% polyester and 35–40% cotton—combines the breathability of cotton with the quick-drying, durable properties of polyester. The polyester fibers wick moisture outward while the cotton fibers provide comfort and airflow.

Why it’s the best choice for work shirts: Blends dry significantly faster than pure cotton, resist wrinkling better, and hold up to heavy-duty washing. They’re also the industry standard for performance workwear in hot climates.

Choosing the Right Shirt for Your Crew

So you’re ordering custom shirts for your landscaping company, your construction crew, or your roofing business. Here’s how to make a smart call based on everything above:

Best Color Choices

White is the clear winner for heat, but it does show dirt and sweat more. If that’s a concern for your crew, light gray or yellow are excellent alternatives—both ranked in the top tier of the Ichinose study and are much more forgiving with wear and tear. Red also performed better than expected and can make a strong brand color.

Colors to Avoid

Black, dark green, and dark navy are the worst performers for outdoor heat. If your brand colors lean dark, consider using those colors on hats, jackets, or cold-weather gear instead—and keeping your summer work shirts in lighter shades.

Fit and Weight

Loose-fitting is cooler than tight-fitting. A loose shirt allows air to circulate between the fabric and your skin, which helps with both convective cooling and sweat evaporation. Lightweight fabrics also retain less heat than thick, heavy ones—even in a light color, a thick shirt will trap more warmth than a thin one.

Custom Shirts That Actually Work in the Heat

When you’re ordering custom-printed shirts for your crew, the print method matters too. Dark shirts require an underbase layer to get vibrant colors to show up—which adds an extra layer of ink between the fabric and your skin. That’s another reason light-colored shirts are the smarter call for outdoor work: your design prints directly onto the fabric with no underbase needed, and you get a cooler shirt at the same time.

At Little 6 Industries, we print custom work shirts using DTF (Direct to Film) transfers—one of the most versatile print methods available. DTF works on both light and dark shirts, produces vibrant, full-color prints, and holds up to heavy washing and wear. But if you have a choice, go light.

The Bottom Line

The color of your work shirt isn’t just a branding decision—it’s a comfort and safety decision. A black shirt in direct Arizona sunlight can run 30°F+ hotter on its surface than a white one. For outdoor workers in construction, landscaping, and similar trades, that heat load adds up over the course of a long day and contributes to heat stress, reduced productivity, and increased risk of heat-related illness.

The fix is simple: choose lighter colors for your summer work shirts. White, yellow, light gray, and red all performed well in controlled studies. Pair that with a breathable cotton-poly blend fabric and a loose fit, and you’ve got a shirt that actually works for the people wearing it.

And if you’re ordering custom shirts for your team—we can help with that.

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