Few things disrupt a polished look more than a sagging shirt collar. This article diagnoses the problem and helps you fix it for good.

The False Fix for Sagging Shirt Collar: Collar Stays
It's natural to assume a floppy collar is caused by, well, the collar itself. Perhaps it's not stiff enough, or not fused well. Perhaps the interlining isn't very good.
The quick (and perhaps natural) fix is collar stays -- those metal or plastic strips that come with many dress shirts. However, you'd be mistaken to think this.
Using collar stays alone won't solve the problem of the sagging shirt collar.

Sagging Shirt Collar Problem: The Placket
Instead, the true cause of a sagging shirt collar is actually lies in the shirt's placket. That's right, the front of the shirt actually causes a collar to sag more than a poor collar itself!
More precisely, the sagging collar is caused by a shirt placket that's not reinforced well.

Wait, What's a Placket?
Glad you asked. As a quick detour, a placket is the piece of material on the front of the shirt where the buttonholes are placed.
The placket, in general, gives the shirt a definite center line. It provides stiffness and, conveniently, allows us to button our dress shirts instead of trying to pull them over our heads.
There are a few different kinds of plackets:

Front Placket:
In this style, the buttonholes are placed on a separate piece of cloth, which is then sewn (or partially fused) onto the rest of the shirt. It's the most common kind for business shirts.

French Placket:
There's no separate fabric here. Instead, the buttons are sewn on the shirt itself. It can look a little cleaner, and perhaps more formal. But, it's a pain to iron.

Fly Front:
Much like the "fly" on your jeans, this covers up the buttons on the shirt. It's quite formal, so you'll occasionally find it on tuxedo shirts.

Learn More
If you'd like to learn more about plackets, or any other topic related to Men's Clothes, be sure to check out the definitive guide to Men's Clothing in our eBook: The Encyclopedia of Men's Clothes

Ways to Stiffen A Shirt Placket
Many bespoke shirt makers have configuration options that include reinforced plackets to help with that sagging shirt collar. However, not everyone can afford a bespoke shirt.
To learn about Andy's favorite bespoke shirt makers, be sure to checkout Andy's Favorite Brands page, detailing his favorite products in each category.