The red knit cap explained

James Cameron’s deep-sea dive: What’s it feel like to go so deep underwater? - Slate Magazine

Director James Cameron successfully completed a 6.8-mile-deep dive to the most remote region of the ocean Sunday and was shown emerging from his submarine in a small knit cap. Jacques Cousteau’s red knit cap was a signature part of his look, which was aped by Bill Murray and his crew in the movie The Life Aquatic With Steve Zissou. Why do underwater explorers wear skullcaps?

Because it’s practically freezing down there. The water temperature at the bottom of the ocean usually hovers around 37 degrees Fahrenheit, and most deep-sea exploration vehicles don’t have climate control. Explorers tend to bring hats, gloves, long johns, and other warm layers, which they pull on as they descend and the temperature drops. Socks and caps are particularly important, as it’s coldest on the floor and ceiling of the submersible. Because of concerns over electrical fires, deep-sea explorers wear natural fibers like cotton and especially wool, which is fire retardant, instead of synthetic fabrics.

Deep-sea divers have been wearing skullcaps, also known as watch caps or seaman’s caps, since long before the adventures of Jacques Cousteau. He may have picked up the style from hard-hat divers—those 19^th-century explorers who wore big copper helmets—who favored red knit caps for decades. The character of Steve Zissou in The Life Aquatic wore an identical cap in homage to Cousteau.