The hole in men’s boxers is called a fly, and its purpose is simple: it gives you quick access to urinate without pulling your waistband down. The opening lets you reach through the front of your underwear and your pants’ zipper at the same time, making trips to the restroom faster and more convenient. That said, only about 20% of men actually use it.
Why It’s Called a Fly
The term “fly” applies to any fabric flap that conceals an opening in clothing. On pants, the fly covers the zipper. On underwear, it serves the same function: a layered opening that provides access while keeping everything covered. The concept dates back centuries. Before elastic waistbands existed, men’s undergarments were secured with long ties, making bathroom breaks a slow, tedious process. Codpieces that buttoned, snapped, or laced shut were one early solution. The modern fly evolved as a faster, simpler alternative.
Boxer shorts themselves emerged in the 1920s, when Everlast’s founder replaced the leather ties on boxing trunks with an elasticized waistband. The resulting loose, comfortable shorts became everyday underwear. The overlapping fly opening carried over from earlier undergarment designs and became a standard feature.
How the Fly Is Designed
Most boxer flies use a simple overlap design: one piece of fabric layers over another, creating a slit you can reach through. There’s no fastener, no zipper. The overlapping fabric stays closed on its own through tension and the natural drape of the material. This works well on boxers specifically because their loose fit makes access easy.
Some boxers add a button to hold the fly shut, which keeps the opening more secure throughout the day. Button fly designs are less likely to shift or gap open during movement, which some men prefer for coverage and peace of mind. Other variations include:
- Side open fly: A double fold of fabric along the side of the front panel, where you reach in from an angle.
- Top open fly: An opening along the waistband area that keeps everything contained more securely below.
Briefs and boxer briefs often use a Y-front fly, a design patented by Cooper’s (now Jockey) in 1935. Instead of a simple horizontal overlap, the Y-front has a seamed, inverted Y-shaped opening that follows the body’s contours more closely. This provides both access and a snugger fit compared to the loose overlap found on traditional boxers.
Why Most Men Don’t Use It
Despite being a standard feature, the fly goes unused by the vast majority of men. Most find it easier to just pull the waistband down rather than navigate through two overlapping layers of fabric (underwear fly plus pants zipper). The fly can also feel awkward to use, especially in snug-fitting boxer briefs where the overlap is tighter. For many men, the fly is more of a legacy design element than a feature they rely on daily.
Boxers Without a Fly
Flyless underwear has been gaining ground in recent years. While open fly designs still dominate the market, closed front underwear is increasingly popular, particularly for athletic use. Without a fly opening, the front panel is a single unbroken piece of fabric that provides more consistent support and less chance of shifting or gapping.
A related trend is the pouch design, where a separate shaped compartment in the front cradles the genitals rather than pressing them flat against the body. These designs address several complaints men have with traditional boxers. The pouch keeps skin separated from the inner thighs, which reduces chafing and friction during exercise or in hot weather. Moisture-wicking fabrics in the pouch area help regulate temperature and reduce sweat buildup. The added support also minimizes the constant need for readjustment that loose boxers are known for.
Pouch designs can also have health benefits. Keeping the area cooler supports healthy sperm production, which is sensitive to excess heat. Adequate support may help prevent issues like testicular torsion. These practical advantages are a big reason why many newer underwear brands have moved away from the traditional fly entirely.
Which Style Works Best
If you actually use the fly for restroom access, traditional boxers with an open overlap are the easiest to use because of their loose fit. A button fly adds security if you find the open version gaps too much during the day. If you never use the fly (which puts you in the majority), a closed front or pouch design will give you better support and a cleaner fit under clothing. For exercise, closed front styles with supportive pouches reduce bouncing and skin irritation far more effectively than a loose pair of boxers with a fly ever could.