You can still carry a garment bag onto an airplane, but a carry on garment bag is a little different than the large hanging jobs of a few years ago. A few years ago, a garment bag was plastic or rip stop nylon cover that fit over your suit hangers. if you brought a garment bag onboard a plane, it would be hung up. Nowadays, a travelling garment bag that you carry on to an airplane has to meet the same requirements as any other piece of carry on luggage. It has to fit in the overhead bin, or under the seat in front of you. This means it has to fold up to a size roughly 12 X 18 X 24 inches. The general guideline is that the length + the width + the height must be equal to or less than 45 inches. This said, airlines vary in their requirements, but you will usually be safe following the 45 inch guideline.
Of course, garment bags that you do not intend to carry on to the plane do not have to meet that size requirement, but they still must be able to be folded and secured with the hangers inside the bag.
Choose a garment bag with a bifold or trifold design so that it can be folded into a manageable size for carrying. It should also have a sturdy handle for carrying in this position, or an attachable shoulder strap. Get a garment bag that has wheels, or can ride “piggyback” on the handle of a larger wheeled suitcase.
Consider your needs. Some garment bags are made specially for suits, while others will hold a variety of garments, including folded shirts, underwear, sweaters and shoes. Look for a bag with inside pockets for storing toiletries or other items. Look for special features that help garments inside the bag resist wrinkles or bunching up.
Be sure the garment bag is made of strong, puncture-resistant material. Make sure the bag has locks so it won’t open when held upside-down, and sturdy zippers or clasps to close it all the way around. Finally, check the warranty. Fine (and expensive) garment bags should have a lifetime warranty.