What Are Trunks, and Who Should Wear Them?

Trunks are the cut most men cannot describe accurately when asked. Some call them "short boxer briefs", which is wrong on the geometry. Some call them "briefs with a leg", which is wrong on the support architecture. The shop staff term that lands closest is "square cut", which captures the visual shape of the garment but stops there. Behind that shape sits a specific structural choice with consequences for which body types and which days the cut actually works on.

The popularity of trunks tracks one thing more than any other, the popularity of slim-fit trousers and shorter shorts. As outerwear got shorter and slimmer across the 2010s, the standard boxer brief leg started to show as a visible fabric line on the mid-thigh under tight trousers, and to peek below shorter shorts. Trunks solved both problems by ending higher on the thigh, with a cleaner profile under modern tailoring. That is the reason the cut exists today, not a desire for less fabric.

This guide takes the four questions men actually ask about trunks. What they are structurally, how they differ from the three other mainstream cuts, who they were designed for, and how they should fit when they are right.

What are trunks underwear, in one line?

Trunks are men's underwear with a square cut that ends on the upper thigh, two to three centimetres higher than a boxer brief, and that gives the same front pouch architecture as a boxer brief without the longer leg. The key structural fact is the position of the leg opening on the body, high enough to disappear under a slim suit trouser, low enough to give a clean visible line and to anchor the front securely.

A trunk is not a "short boxer brief" in the strict sense. The cut is engineered for the higher leg position rather than scaled down from a longer cut. The fabric panels at the front and the seat are shaped for the shorter geometry, which keeps the support architecture intact even though the leg is shorter. The SAXX trunks range is built on the same BallPark Pouch® and Flat Out Seams® construction as the boxer brief range, with the panels cut to the trunks geometry.

How do trunks differ from boxer briefs, briefs and boxers?

Trunks sit between briefs and boxer briefs on the leg length scale, and between boxers and briefs on the support scale. The decisive variables are leg length, level of support, and surface contact with the thigh. The table below maps the four mainstream cuts on these variables so you can see where trunks sit, not in the abstract, but against the cuts most men have already worn.

The two cuts most often confused with trunks are briefs and boxer briefs. The difference with briefs is visible immediately, trunks have a leg, briefs do not. The difference with boxer briefs is subtler, two to three centimetres of leg fabric, but the consequence on a real day is bigger than the difference looks. The longer-form treatment of each cut sits in the complete cuts comparison, and the dedicated SAXX briefs range is the test pair when support without leg coverage is the requirement.

Who should wear trunks?

Trunks were designed around two converging trends, slimmer outerwear and the male body that wears it well. A slim or average build with narrow hips fits the trunks geometry naturally. The waistband sits cleanly on the hip without the band rolling forward on a wider stomach, and the short leg sits cleanly on the thigh without the fabric riding up on a longer leg.

A second clear case is the man with thighs that do not touch when standing. The classic boxer brief argument, that the leg fabric protects the inner thigh, does not apply to him. The two centimetres of extra leg fabric on a boxer brief becomes surplus, visible under tight trousers and warm under heavier trousers. Trunks remove that surplus while keeping the support structure of the boxer brief intact, which is the cleanest win for this body type.

A third case is the man whose daily uniform is slim-fit suit trousers or chinos. The mid-thigh leg of a boxer brief produces a faint horizontal line on slim trousers, visible in side-light. Trunks end above that line, which removes the issue. For dress-code-driven roles, this is the differentiator that makes trunks worth a place in the rotation even on a body type that wears boxer briefs the rest of the week.

Who probably should not wear trunks?

Trunks fail in three predictable cases. The first is the stockier build, where the thighs touch when standing. The trunks leg ends above the inner thigh contact zone, so it leaves the skin-on-skin friction in place. A long leg boxer brief, or even a standard boxer brief, is the safer cut. The mechanism behind that inner thigh problem is covered in detail with long leg boxer briefs as the cut built to manage it.

The second case is the athletic or chafing-prone day. A long walking day, a six-mile training run, a half-marathon, all generate friction at a section of the thigh that a trunks leg simply does not reach. For these days, a boxer brief or long leg variant in a technical fabric is the answer. The SAXX boxer briefs range remains the everyday default for most men, with the trunks cut reserved for the specific use cases above.

The third case is the wardrobe context. Under loose-cut trousers, jeans with a relaxed leg, or workwear, the short trunks leg adds no visible benefit, and the longer boxer brief leg gives better thigh contact and stability. Trunks pay off precisely when the outerwear is slim enough to expose the underwear leg line, which is increasingly common in modern menswear but is not a daily reality for every man.

What are the right occasions for trunks?

Trunks earn their place in three concrete situations on a man's week. They are the right cut under slim-fit suit trousers and modern tailored cuts, where the boxer brief leg shows. They are the right cut under shorter shorts, including modern tailored shorts and slim swim trunks, where a longer underwear leg would be visible below. And they are the right cut on hot office days, where the lighter overall fabric surface keeps the lower body cooler than a fuller boxer brief.

Outside these three contexts, trunks are a personal preference rather than a structural requirement. Most men who wear them in everyday rotation do so because the silhouette feels cleaner under their usual clothes, not because the cut solves a specific functional problem. There is nothing wrong with that, but the cut is purchased for aesthetics in that case, which is a useful thing to know before buying multiple pairs.

If you want a starting point that pre-filters for the structural quality side, the comfortable men's underwear selection includes trunks built on the same pouch and seam construction as the rest of the SAXX range, so the cosmetic choice does not come at the cost of all-day comfort.

How should trunks fit?

Trunks should sit snug on the upper thigh without leaving a red mark, with the waistband flat on the hip line, and with the front pouch holding without bulk. The fit standard is closer to a brief than to a boxer brief, with less margin for sizing up. A trunk that is one size too large bunches on the thigh and the seat in a way that boxer briefs hide better with their longer leg.

Three fit signals matter most. The leg opening should sit smoothly without rolling onto itself when you sit down. The seat should follow the buttocks without creating a horizontal fold under heavier trousers. The waistband should disappear under your usual waistband within an hour of putting it on, which is the single most reliable test for any cut, trunks included.

The construction stack that holds trunks fit consistently across body types is the same as the rest of the SAXX range, BallPark Pouch®, Three-D Fit®, Flat Out Seams® and DropTemp® where applicable. The full description sits on the SAXX technologies page.

Frequently asked questions