5 Reasons Why Running Shorts Have Built-In Underwear

Nowadays, it’s common to find running shorts equipped with a liner. But why do these running shorts have underwear inside them?

The main purpose of the built-underwear (liner) in running shorts is to wick away sweat and moisture in the crotch during a run. It also prevents chafing since the fabric is held tightly against the skin, causing little to no friction of the material over the skin.

In this post, we will explain the 5 reasons why running shorts have built-in underwear. We will also share with you the best way to utilize it properly.

Why Do Running Shorts Have Built-In Underwear?

There are five important functions for a liner in running shorts.

In addition to wicking sweat away during exercises, a liner offers support for both men and women without being too constricting because it is made of lightweight materials.

Built-in underwear in running shorts also prevents chafing and provides one less layer below the belt to keep you cool and comfortable, especially during warm and humid days.

Here are the five benefits of built-in underwear explained:

1. Wicks sweat and moisture away

The primary function of the liner inside running shorts is to wick away sweat and moisture from your crotch. As you perspire during a run, the liner, which is made of moisture-wicking fabric, will allow sweat and moisture to evaporate.

Additionally, the material running shorts are made from is exceptionally lightweight and generally designed in such a way as to allow maximum ventilation (using split side legs).

Some better options used in high-performance sports clothing are technical fabrics that blend various materials—like polyester, elastane, spandex, and nylon.

These materials give comfort through breathability, drying, and cooling capabilities. As a result, the built-in underwear will make you feel cooler and drier during a run.

2. Offers support for men’s genitals

The second reason why most running shorts have a built-in liner is to provide some support and motion control. For men, it is designed to provide the right support for the genitals.

Our bodies are very well adapted to running.

When running longer distances, the male body redirects blood flow to other areas and the scrotum and penis retract or shrink a little (similar to entering cold water).

But before this short-term physiological effect happens, the liners inside running shorts can protect your modesty and keep your dangly bits from showing up in all the wrong places.

Even during a run, the liners in running shorts would be able to provide the right amount of support without too much compression because the materials are very lightweight.

3. Prevent women’s shorts from riding up

On the other hand, most women hate shorts that ride up, especially when working out.

However, there’s practically no way the underwear can ride up since it is built into the running shorts unless the shorts don’t fit properly.

If you have ever experienced having to pull out your shorts or underwear because your butt is “eating” them, then wearing lined shorts would definitely solve the issue.

You’ll save yourself from the embarrassment of pulling your shorts with underwear or boxer briefs down in the middle of the run to arrange its fit.

4. Prevents chafing

Another benefit of wearing running shorts with built-in underwear is to prevent chafing. 

With liners, the fabric is held tightly against the skin, so there’s little to no movement of the material over the skin the way there might be with looser-fitting shorts.

The movement, which causes constant friction and rubbing, is what causes the chafing. So if the material doesn’t move over the skin, there would be no chafing.

5. One less layer in the heat

Some runners like to wear tights, especially on cold days. We agree that they can be comfortable. On warmer days, however, we’ve always felt like less is more.

Because lined shorts already serve as your underwear, there’s no reason for you to find good running underwear to wear under your running shorts.

If you can manage to wear the apparel without separate underwear, it will feel like one less layer in the heat, especially during warm and humid days.

The built-in underwear is made of thin and loose-knit fabric, therefore, air flows into your crotch area better. This helps you feel fresh and cool even on longer runs.

Frequently Asked Questions on Running Shorts and Liners

Here are some of the frequently asked questions on running shorts and their built-in underwear. We will add new questions, so bookmark this page if you find this interesting.

1. Are you supposed to wear underwear with running shorts?

Contrary to popular belief, you’re not supposed to wear underwear under your running shorts. A liner (built-in underwear) is often provided to keep you secure and comfortable.

The liner inside running shorts can keep you cool, wick away sweat, and also prevent chafing often caused by wearing another layer of underwear underneath.

However, it all comes down to what makes you most comfortable. If you feel like wearing underwear with lined running shorts, then by all means, go for it.

2. Can you cut the liner from running shorts?

You can cut the liner from running shorts by pulling out the built-in underwear from the inside and cutting it along the nearest line to where they’re sewn.

Also, be careful when trying to cut the liner because some shorts have hidden pockets. If the shorts have pockets, cut around the pockets at the top seam and sew it down in place.

In some cases, it is part of the structural integrity of the running shorts and they won’t stay in place without it and in others, they can be removed easily with no ill effects on fit.

Since some people find built-in underwear in running shorts uncomfortable, we would recommend buying one lined and unlined shorts and trying which one fits you best.

You may also be interested in: