This article first appeared on Triathlete.

Some endurance athletes swear by visors on a run, insisting they make them feel cooler, while others believe a hat is the smartest headwear option because it allows them to put ice on their heads at aid stations. Mat Steinmetz, the founder of and a coach who has worked with top-level names such as three-time Kona champ Craig Alexander on his heat management, suggests a visor in most cases, as fabric typically interferes with the evaporative effect of sweating.

Hats can protect your scalp from radiant heat, but they can also lessen evaporative and convection cooling. “Most research shows that although skin head temperature increases and you feel hot, core body temperature does not,” Steinmetz says. “A cool head, however, does influence comfort, as the head impacts whole body thermal sensation”—as in, if you think you feel cool, it could make your whole body feel cool, even if your core temperature isn’t actually any lower. (Note that if you put ice in your hat, it could cause vasoconstriction, or narrowing of blood vessels, and reduce heat loss, which would have the opposite desired effect, Steinmetz says. It won’t reduce your core temperature, but it could improve your comfort level or perception of heat—at least until it melts.)

If you choose a hat, Steinmetz recommends a full mesh hat that allows air to pass through. “I would look for a material that doesn’t absorb moisture other than the sweatband to reduce becoming weighted and a nuisance,” he says. Look for mostly white, and popular athlete-specific trucker hats are a good option.

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If you opt for a visor, select a white visor with a black under-brim (to reduce glare). Look for the same qualities as the hat in regards to absorbing moisture—you don’t want the visor to get heavy and uncomfortable.

“In the end, I think it comes down to personal preference,” Steinmetz says. “There is a lot that goes into thermoregulation in hot and humid environments. … You should choose what you perceive as feeling more comfortable. Your head, neck or face feeling cool has a big impact on your comfort level, even if it doesn’t reduce core temperature.”

READ MORE: 4 Run-Friendly Headwear Options From the Editors of Triathlete