I never pay for checked bags because this backpack-duffel hybrid can hold nearly 2 weeks' worth of clothes

Insider Picks writes about products and services to help you navigate when shopping online. Insider, Inc. receives a commission from our affiliate partners when you buy through our links, but our reporting and recommendations are always independent and objective.I've been using the Cotopaxi Allpa 35 ($190) for two years as my go-to luggage for domestic and international trips.It's a hybrid backpack-duffel carry-on that's tough, comfortable, and a seemingly bottomless pit for belongings.Recently, it held two weeks' worth of clothes for a European trip — and cost me zero in checked-bag fees.Since joining the Insider Picks team in 2017, I've tested thousands of products. This means that in the last two years, I've replaced my own skin care, robes, exercise leggings, hot tools, and credit cards with the superior options I've discovered along the way. But, in the last two years, I've had one remaining constant: my carry-on travel bag.The Cotopaxi Allpa 35 ($190) has been my reigning champion of luggage for two years of product testing. It's tough, comfortable, and seemingly bottomless — like the magic handbag Hermione Granger stuffs outdoor tents and spellbooks into. And it's perfectly sized for a carry-on, which means I can save on checked-luggage airline fees, lost bags, and tedious carousel lines without needing to pack fewer outfits. It's easily the best travel accessory I've found in years.CapacityThe biggest perk to the Allpa 35 is spaciousness. The 35 in its name alludes to 35 liters, a nod to its capacity. It's fit enough gear for a nearly two-week-long European vacation as well as both legs of a trip that started with snowstorms in Minnesota and ended beach-hopping in Belize — and I've never had a problem fitting it into the overhead compartment. I'm also not a particularly lean packer. You still have to be selective when relying solely on a carry-on bag, but there are some easy ways to optimize. I typically use PackPoint, an app which analyzes the weather at your destination and planned activities, to spit out a first draft packing list — mostly so I don't forget adapters abroad or go unchallenged when bringing three sweaters but zero jackets. Once I have my list, I roll my clothes to fit more than folding.Since it's a soft shell, the Allpa 35 is more malleable than most suitcases; I've definitely pushed it beyond its promised limits before. And since it's a carry-on, I've been able to fit overflow or bulk items like shoes or a winter coat in a larger “personal item” for no additional cost. Organization This thing is well-designed. It has just enough pockets — one for everything you need, and none that make you despise them for simply taking up space. The front of the bag has a roomy top pocket you can get into without unzipping the main compartment that's great for travel accessories like headphones, a passport, and a wallet. Inside are two deep compartments, a shallow hidden pocket at the joint of the two, and two subdivided pockets for essentials like makeup, passports, and any other small accessory at the top. There's also a collapsible mesh laundry bag and a nylon shoe bag included.The Allpa 35 opens like a suitcase so you don't have to shove your arm down to the bottom as you do with a backpacking pack. It also has an external zipper that leads inside the bag like a slit on one side, and a separate laptop and tablet compartment on the other. For safety, all external zippers have theft-proof webbing sewn across the openings.ComfortabilitySince Cotopaxi is an outdoor brand, the Allpa 35 uses the same tech that makes heavy backpacking packs comfortable for miles, like a low-profile harness which helps distribute weight efficiently. I've found my Allpa heavy, but I've never found it uncomfortable. It has contoured, cushioned shoulder straps, a padded hip belt, and a breathable air-mesh back panel to keep you from feeling hot or sweaty. Since the straps can be tucked away, you can also use the bag as a duffel, or ignore the (semi-dorky but very helpful) padded hip belt — as I do. DurabilityI've been using the Allpa 35 for two years of frequent travel, and it looks no worse for wear. It performs the same way it did when it was new. The blend of tough, TPU-coated polyester and ballistic nylon paneling mean this thing should happily endure years of battering.The bottom lineAll in all, I'm just as impressed with it now as I was when I first tested it. It looks the same as it did on day one. It's comfortable enough for long airport trips, and its cavernous compartments mean I never pay for checked bags anymore because I can fit enough gear to suffice for a two-week-long trip in a carry-on alone.If you're looking for a durable, exceptionally well-designed bag that you can use for years to come, I highly recommend checking this one out.Buy the Cotopaxi Allpa 35 at Cotopaxi, REI, and Backcountry for $190