A gym bag is opened and closed more often than any other bag anyone owns, loaded unevenly, and put down on wet floors. It fails in a predictable order, and knowing that order tells you what to check.
The zip goes first
A bag opened twice a day is a bag whose main zip cycles seven hundred times a year. Chunky moulded plastic zips and branded metal coil zips both last; thin unbranded coil zips do not. A double slider is worth having because it lets you open from either end.
Check whether the zip is backed by a fabric flap. Unbacked zips catch contents, which is what eventually pulls teeth out of the tape.
Then the base
A bag put on changing room floors and in car boots wears through at the corners. A reinforced base panel, ideally in a heavier denier fabric or with moulded feet, is the difference between three years and one.
Feet also keep the base out of standing water, which is what soaks contents in a wet changing room.
Then the strap attachment
Straps rarely break; the point where they attach to the bag does. Bar-tacked stitching over a reinforcement patch is what to look for, and it is visible in a close photograph. A strap attached to a thin webbing loop stitched to the body panel will eventually tear the panel.
A detachable shoulder strap with a padded section is more comfortable and one more thing to lose. Fixed straps are simpler.
Denier is a useful shorthand
Fabric weight is given in denier - 300D is light, 600D is a common durable middle ground, 900D and above is heavy duty. Higher denier is tougher and heavier; for a bag carried daily, 600D is usually the right compromise.
Coated fabrics resist water at the surface. Nothing short of a welded dry bag is genuinely waterproof, and bags advertised as such rarely are at the zip.
The wet compartment question
A separate ventilated compartment for wet kit is the single most useful feature on a gym bag, and the reason is not smell but the rest of the contents. Without one, damp kit sits against clean clothes for hours.
Ventilated means mesh panels or grommets. A sealed plastic-lined pocket keeps water in and grows mould.
Shoe compartments: sometimes worth it
A dedicated shoe compartment protects clothes and takes volume permanently, whether or not shoes are in it. For a bag used only for the gym it is useful; for one that doubles as a weekend bag, a removable shoe bag is more flexible.
Check the stated shoe size the compartment fits. Many are sized around a US 9 and will not take larger.
Volume, honestly assessed
Thirty to forty litres covers kit, shoes, a towel and a change of clothes. Fifty litres is a weekend bag. Bags are quoted in litres and it is worth comparing against a bag you already own rather than trying to imagine the number.
A bag larger than you need gets filled anyway and carried on one shoulder, which is how shoulders get sore.
Carrying it any distance
Beyond about a fifteen-minute walk, a duffel on one shoulder becomes uncomfortable regardless of padding. Convertible bags with backpack straps solve this and add bulk. If the commute is on foot or by bike, that feature is the deciding one.
Grab handles that meet in the middle with a wrap are more comfortable than two separate handles.
Cleaning it
Empty it fully once a week and leave it open to dry. Most bags can be sponged out; few should go in a washing machine, which delaminates coatings and destroys structure.
We list capacity, fabric denier, compartment layout and strap configuration on every bag we carry, because those are the four that decide whether a bag survives a year of daily use.