The hole in men’s underwear is a fly, and it’s there so you can urinate without pulling your waistband down. It provides a quick-access opening through the front of the fabric, letting you unzip and go without undoing your belt or lowering your pants and underwear entirely. Simple as that.
But there’s more to the story than basic bathroom convenience. The fly also plays a role in ventilation, support, and overall comfort. And despite being a standard feature for nearly a century, most men don’t actually use it.
Why the Fly Exists
The fly’s primary job is speed and discretion at the urinal. Without one, you’d need to pull your underwear down completely for every bathroom break, which means undoing your belt, adjusting your pants, and doing the whole routine in reverse afterward. The fly cuts that process short. You unzip, reach through the opening, and you’re done in seconds.
Beyond bathroom access, the fly opening adds airflow. That extra layer separation in the front panel lets air circulate, which helps with temperature regulation and reduces moisture buildup throughout the day. For a body part that sits in a warm, enclosed space for hours at a time, even a small increase in ventilation makes a difference.
Most Men Don’t Actually Use It
Here’s the twist: only about 1 in 5 men regularly use the fly for its intended purpose. The majority just pull the waistband down when using the restroom. Some find it awkward to navigate the overlapping fabric layers. Others wear pants with easy enough access that the fly feels unnecessary. And for men wearing jeans or casual pants without a zipper fly of their own, the underwear fly doesn’t help much anyway.
So the fly remains a standard design feature that most of its users quietly ignore. It’s one of those things that exists because it’s always existed, even as habits have shifted.
How the Fly Got Its Shape
Men’s underwear didn’t always have a fly. Until the 1930s, most men’s undergarments were loose-fitting, full-body garments without a dedicated front opening. That changed in 1935 when the American company Cooper’s (later Jockey) launched the Y-front brief. It featured a patented overlapping inverted Y-shaped seamed fly opening, and it was revolutionary. The design provided both easy access and structured support in a single garment, something men’s underwear had never offered before.
The Y-front was also notable for being one of the first undergarments to openly acknowledge male anatomy through its construction. The shaped seams around the fly area drew attention to the body rather than concealing it, a sharp departure from everything that came before. That basic overlapping-panel concept has remained the standard fly design for nearly 90 years.
Vertical, Horizontal, and Pouch Designs
Not all flies work the same way. The traditional vertical fly uses overlapping fabric panels arranged top to bottom, which you spread apart to access the opening. It’s the most common design and the one most people picture when they think of men’s underwear.
A horizontal fly runs side to side instead. Many men find this orientation more intuitive to use, and it provides better security against accidental exposure since the fabric naturally stays closed with body pressure. Some newer designs use an X-shaped fly that combines both directions for easier access.
Then there’s the modern pouch design, which reshapes the entire front panel into a three-dimensional pocket rather than relying on flat overlapping fabric. A proper contoured pouch lifts everything away from the legs, which prevents skin-on-skin sticking, reduces heat buildup, and provides natural support without compression. Some pouch designs incorporate a functional fly within the pouch structure, while others skip the fly entirely in favor of a seamless, supportive fit.
Why Some Underwear Skips the Fly Entirely
A growing number of brands now sell underwear with no fly at all. This is especially common in athletic and performance underwear, where a seamless front panel offers a smoother fit and eliminates any risk of chafing from overlapping fabric edges. Without a fly opening, designers can also use that space for continuous stretch fabric that moves with your body during exercise.
The tradeoff is straightforward: no-fly designs prioritize support and streamlined comfort, while fly designs prioritize bathroom convenience. For men who never used the fly anyway (which, again, is most men), going without one doesn’t change their daily routine at all. For the minority who rely on it, a fly-free pair can feel like a real inconvenience, especially when wearing a suit or tucked-in shirt where pulling down the waistband means untucking and readjusting everything.
Your choice between fly and no-fly comes down to how you dress and how you use the restroom. If you wear business clothes with a belt and tucked shirt, a functional fly saves you real time and hassle. If you wear athletic wear or casual clothes with an elastic waist, you may never miss it.