Scoring a complimentary upgrade to first class is never guaranteed, but flight attendants say your appearance can sometimes play a role when airlines need to move passengers into premium seats.

According to several cabin crew members, travelers who dress in smart, neat clothing often leave a better impression than those wearing overly casual outfits. While designer labels aren't necessary, looking polished can signal that you're a frequent traveler and fit the atmosphere of the premium cabin.

For both men and women, business-casual attire tends to be the safest choice. Think tailored trousers, chinos, button-down shirts, blazers, cardigans, dresses, or clean leather sneakers. On the other hand, clothing such as pajamas, flip-flops, worn-out T-shirts, or overly casual athletic wear may reduce your chances if an upgrade opportunity arises.

Of course, your clothing is only one small factor. Complimentary upgrades are typically based on availability, airline status, loyalty programs, operational needs, and ticket type. Even the best outfit won't override those priorities.

That said, dressing smartly can still be worthwhile. You'll often feel more comfortable in airport lounges, make a stronger first impression, and be prepared for business meetings or dinner immediately after landing.

The Takeaway: Dressing well won't guarantee a free first-class upgrade, but a polished, business-casual outfit may improve your chances if the airline needs to move passengers into premium seats.