At the end of the day, any duffel bag that's large enough to accommodate your belongings and compact enough to meet your airline's carry-on size regulations will work. While most airlines accept carry-on bags smaller than 22 x 14 x 9 inches, size regulations can vary from airline to airline, so it's absolutely essential that you check with your preferred airlines before choosing a bag. Similarly, you should seek out a bag with lightweight construction to help keep your duffel under airline weight limits. Also, keep in mind that a soft bag is easier to cram into an overhead bin on crowded flights. There’s nothing worse than having to check your carry-on bag at the last minute.