Common sense says that dark cycling apparel will be hotter on sunny days. But what does science say? Unfortunately, not much. There’s very little concrete data on the role color plays in keeping you comfortable on a bike. So, Travis did some research, read some papers, and asked some brands to chime in. One of them actually did!
There’s an exhausting level of optimization in bike design these days. And I am here for it. If a new feature or component will improve my ride (in a way that I value), I want it. Same goes for apparel. I wear long, baggy shorts on the descents for protection, but I peel them off before long climbs for that friction-free lycra experience. I’ll also shed my hip pack, gloves, and sometimes even my helmet if I want to feel truly unencumbered. And I exclusively wear loose-fitting, long-sleeve shirts. Especially in the summer. They trap cool air, keep the sun off my arms, and add full-coverage insulation on days when I might need a windbreaker in the early morning or late evening. I also prefer those tops to be light-colored. I figured that’s just common sense. I learned in grade school that dark colors absorb the sun’s energy while light colors reflect it.
But look at most cycling brands’ catalogs, and there are usually many more dark-colored options than light-colored, especially in the men’s section. It’s not hard to guess why that is. Dark clothes are more fashionable, and thus, more marketable. Plus, they don’t show dirt. But let’s be real. I’m roaming the woods wearing a fanny pack and a styrofoam hat. I look ridiculous no matter how clean or dark my clothes are. So, I figured this was yet more proof that I’m smarter than half the bike industry, until I came across an interesting study involving the traditional black robes often worn by the nomadic Bedouin tribes of the Arabian Peninsula and North Africa.
Although Bedouin garb is sometimes white or light gray, many Bedouins wear black or dark blue. The study was published in the journal, Nature. It’s almost 45 years old, was conducted on only one person, and didn’t control for a few variables that are important for a cyclist. But it’s interesting nonetheless. It found that, in certain conditions, dark colors have no meaningful impact on the temperature of air between clothes and skin.
Just to set expectations, I don’t have the vocabulary to fully understand this study. Even the difference between “heat” and “temperature” kinda makes my head spin. But basically, the study included four types of outfits: black robes, white robes, a western army uniform, and finally, just a pair of shorts. Researchers put a man in each outfit and took measurements internally and externally while he stood in the sun for a period of time. The ambient temperature varied from 95° to 115° Fahrenheit, and wind speeds varied from 0 to 9 MPH. Although the external surface temperature of the black robes averaged 10° warmer than that of the white robes, internal temperatures on both would reliably match whatever the ambient external temperature was.
The study’s authors stop short of exploring exactly how that occurred. One of their guesses is that there’s a “chimney effect,” where the increased heat gain of the black robes creates an upward flow of warm air, which pulls in the cooler outside air from beneath the robe. The other guess is that there was just enough wind to allow the robes to flap, pulling in cool air and pushing out warm air before it had time to heat up the skin.
Either way, this study wasn’t enough to convince me to bring all my dark jerseys out of retirement. For one thing, they aren’t robes. So, the mechanics of air circulation are probably different. Also, the 0- to 9-MPH range of wind speeds present in the study is pretty wide. I’m often climbing through the windless doldrums, moving at 3 MPH. But this study is the most thorough one I could find. It’s the primary reference for dozens of clickbait articles all over the internet … and I guess my article is now one of them. So, in hopes of elevating it above mere clickbait, I also reached out to a handful of cycling and outdoor apparel brands asking if they’re conducting studies specifically aimed at cyclists. Spoiler alert: They aren’t.
To be fair, I did not reach out to every outdoor apparel brand on Earth. There may be a dedicated product manager somewhere, posted up in the desert with a Pantone chart and a laser thermometer. If so, I’m sorry I missed you. But I did hear back from five major brands, and only one of them had anything meaningful to share. I’m not gonna call out the brands who didn’t, though. Clearly, they’re not alone.
But big thanks to Pearl Izumi, who gave me some pretty interesting info.
“This is something we have to think about all of the time, since black and dark colors are so fashionable in the cycling industry,” begins Matt Kent, materials developer at Pearl Izumi. At first, the word “fashionable” put me on the defensive. But he followed it with a bespoke three-page document, complete with bold subheadings and bullet points. Kent outlined the many interconnected factors that affect a rider’s temperature, and what role apparel color does or doesn’t play.
It all starts with how the body sheds heat through the skin, which is a joint effort shared between blood and sweat. Blood vessels just beneath the skin’s surface will dilate, speeding up cooling of the blood. Meanwhile, sweat will accumulate and evaporate, bringing excess heat along with it. It’s a pretty straightforward mechanical process, and it’s happening right there on the surface. So, our clothes can potentially play a role. “The question is simply ‘how much?’,” Kent explains. “Unfortunately, without balancing certain features, you end up making tradeoffs in opting for one approach to improving thermal comfort vs another.”
With this shaping up to be an “it’s not that simple” kind of thing, Kent steps away from color for a second. “The thinner the fabric, the less heat can build up within it,” he says. “Our black bib shorts will hold much more heat than our black jerseys. Technically, they might reach the same temperature, but it will take less energy from the body or environment to cool off the jersey than the shorts.” So, fabric weight can offset (or exacerbate) the effects of fabric color. But of course, there’s a limit. Even the lightest bib shorts require a heavier fabric than a jersey. And that’s an apt comparison because how tight or loose a garment fits plays a role as well.
“The more contact between the skin and the fabric, the greater the influence of the fabric temperature,” Kent explains. He mentions silk is a good illustrator of this. Its uniquely soft and flexible fibers will drape more closely to your skin and pull more heat away. “Of course, this means that the opposite is true in situations where the fabric is warmer than the skin.” Loose-fitting clothes are in less contact with the skin, and also allow for more air circulation through areas that are now effectively shaded. “This is great for slower situations,” says Kent. “But there is a large tradeoff considering the aerodynamic penalties of baggy fabrics.”
I expected aerodynamics would eventually enter the chat, but it’s not a huge factor in my world. What is a huge factor is UPF, pun intended. That’s something I didn’t expect until I started researching this. “The darker the color the more solar radiation is absorbed by the fabric,” Kent explains. “This means that you will be protected more from the sun in a darker fabric than a lighter one, given that the fabrics are identical and that the construction allows some light to pass through.”
My long-sleeve lifestyle isn’t just about temperature. It’s about protection. The less surface area requiring sunscreen re-application, the better. But I guess I should pay attention to the UPF rating of my clothes. Not just because I want to stay protected, but because of course, it’s interrelated with color and comfort. “It is therefore necessary to balance the material construction to reduce the light that passes through, even in a lighter color since not doing so will negate the benefit of having a lighter colored fabric.”
Kent continued to pile on the variables. Like the fact that heat gained through solar radiation is less of a factor in humid climates, where a lot of the heat is gained through the more conductive wet atmosphere. Or that there are fabric treatments that improve cooling or UPF rating. Or in a real mindbender, I learned that the body loses more heat through radiation than convection or conduction. So, if this isn’t accounted for in the fabric, the heat-blocking effect of a light-colored garment will also work in reverse, bouncing trapped body heat back at the skin.
Before leading me down all these rabbit holes, Kent at least validated that grade-school logic at the heart of my wardrobe choice. “At the most basic level,” he begins, “if you have two identical and untreated fabrics, one white and the other black, the black one will always warm up more than the white when exposed to sunlight.” But that’s not the same as saying that light-colored fabrics will keep the majority of cyclists cooler than dark-colored fabrics. And I understand why there aren’t more studies on the subject. “From a data gathering perspective, we typically do not have the bandwidth to perform specific testing on this topic.” Kent says. “Especially as you can see that testing one element will not necessarily provide the entire picture needed for an informed product decision.”
This is not how I hoped this story would go. I guess I do feel mildly validated in my preference for lighter colors, but I no longer think it makes me smarter than half of the bike industry. Maybe it’s the same as any other preference, like tire pressure or handlebar width or suspension travel. It depends on your specific situation.
I’ll still go for my collection of white-long-sleeve shirts when I know I have a long slog up an exposed 9% fire road. But maybe I won’t take it on a muggy North Carolina vaycay, or a breezy coastal overnighter, or honestly, anywhere in public. This thing shows a lot of dirt.
