You can absolutely take a Yeti backpack cooler on a plane, but how you use it depends on TSA regulations and airline size limits. Most Yeti backpack coolers, like the Hopper M12 or M20, are sized to fit within the standard carry-on dimensions of major airlines (usually around 22 x 14 x 9 inches), meaning you can use it as your main carry-on bag or a personal item if it fits under the seat. The most critical factor is the contents. TSA prohibits "slushy" or melted ice; therefore, you cannot have loose ice or water inside the cooler when going through security. You must use completely frozen gel packs or ice packs. If the gel packs have started to melt and are "squishy" at the checkpoint, security may confiscate them under the 3.4oz liquid rule. Once you have cleared security, you can often ask a restaurant or flight attendant for ice to fill the cooler for the flight. If you choose to check the Yeti as luggage, it is rugged enough to survive, but ensure all zippers are fully closed and any straps are tucked away to prevent them from getting caught in the airport's conveyor belts.