The best carry-on backpacks

Three groups, clearly. People flying carriers that weigh cabin baggage - a frameless pack leaves far more of a 7 kg allowance for clothes. People traveling somewhere with stairs - European stations without lifts, old towns with cobbles, anywhere a wheel is a liability. And people who move between places often, because a pack gets carried up a flight of stairs in one motion where a case is a two-stage operation.

Who should not: anyone with back, shoulder or neck problems, for whom this is not a preference but a medical question; anyone flying long US domestic routes on full-service carriers where nothing is weighed and terminals are flat; and anyone who packs heavy, because a pack's weight is on your body rather than on the floor.

Four criteria, in order. Does it fit the carry-on envelope as stated, and does it compress when stuffed. Does it open like a suitcase - top-loading packs are genuinely worse to live out of. Does the harness stow, because a pack checked with straps exposed comes back damaged. And empty weight, which is the main advantage packs hold over wheeled bags and which some structured designs give away entirely.

We have not carried these through an airport ourselves and do not run a testing lab. Comfort and durability findings come from published hands-on testing by named reviewers; our methodology explains exactly what that means.

• Hiking packs used as travel bags. Top-loading, tapered, and covered in straps that catch in baggage systems. They are excellent at the thing they are for, which is not this.
• Packs above 45 liters sold as carry-on. Volume that large almost never fits the dimensional envelope once packed, whatever the listing claims.
• Packs with fixed external water bottle pockets. They protrude, they count toward the airline measurement, and they are the first thing a sizer catches.
• Wheeled convertible packs. They carry the weight penalty of wheels and the discomfort of a pack, and are usually worse than either done properly.

1. Check the dimensions, not the liters. Volume is not a size limit. Compare stated length, width and depth against your airline's published figure.
2. Insist on a clamshell. Top-loaders are miserable to live out of and this is the single biggest usability difference in the category.
3. Check the harness stows. If you ever gate-check it, exposed straps are what gets torn off.
4. Weigh it empty. A structured pack can weigh as much as a light wheeled case, which removes the main reason to choose it.
5. Try it loaded if you can. Torso length matters more than any spec - a pack that fits badly is uncomfortable at any weight.

A wheeled case is packed flat and the weight sits on the floor. A pack is packed in layers and the weight sits on you, which means the order matters: heavy items go close to your back and roughly at shoulder-blade height, not at the bottom. A pack loaded bottom-heavy pulls you backward and is genuinely more tiring to carry.

Packing cubes matter more in a pack than in a suitcase, because a pack has no rigid shape to hold things in place - cubes turn a shifting heap into stable blocks. Compression cubes are worth it here too, since the bulky layers you would otherwise carry loose are exactly what they work on.