Why Do Running Shorts Have Built-In Undies?

If you’ve ever picked up a pair of men’s running shorts and noticed the built-in underwear, you might have wondered why they’re there in the first place. Are they actually necessary, or just a quirky design choice? Let’s break it down.

The Purpose of Built-In Liners

The main reason running shorts come with a built-in liner is comfort. Shorts with liner are designed to eliminate the need for separate underwear, reducing bulk and the risk of chafing. When you're logging miles, the last thing you want is fabric bunching up or seams irritating your skin. Liners help wick moisture, improve airflow, and offer light support, keeping you dry and comfortable throughout your run.

Why It Matters for Performance

Lightweight, breathable liners aren’t just about comfort — they also enhance performance. By cutting down on excess fabric, your body can move more freely. Whether you prefer 5 inch shorts for a balance of coverage and mobility or shorter lengths for race days, built-in liners help you focus on your stride, not your gear.

Are Lined Shorts for Everyone?

Not every runner loves liners, and that’s okay. Some athletes prefer to wear their own performance underwear underneath looser shorts, especially for activities like cross-training or weightlifting. But for distance running, many find that shorts with built-in liners offer the best combo of simplicity, support, and sweat management.

Final Thoughts

So, why do running shorts have built-in undies? It’s all about reducing irritation, improving breathability, and enhancing your run. If you’re building a running wardrobe, make sure to include a few pairs of lined shorts, especially those 5 inch shorts that offer just the right amount of coverage without slowing you down. And for versatile, performance-driven picks, check out men's athletic shorts collections designed to move with you, mile after mile.