The brass hook that promised a miracle
First door hamper I bought had a brass hook rated for 30 pounds. The bag itself weighed 2 pounds empty. It lasted four days before the hook bent and the whole thing crashed onto the floor at 2am, waking up my dog. The bag was fine. The hook was garbage. I returned it and bought two more, expecting the same pattern. I was half right.
What actually matters: the gap under the door
Every hamper I tried hooked over the top edge of the door. You'd think all doors are the same, but they're not. My hallway door has a 1/4-inch gap between the door and the frame. The thicker the hook, the tighter it sits. One hamper came with a hook so thick it wouldn't slide over the door without scraping the paint. I fixed it with a rubber mallet. You shouldn't need a rubber mallet.
So before you even look at the fabric, measure the gap. If your door sits flush against the frame with barely a sliver, get a hammer or get a different hook design. The ones that have a C-shaped clip that hooks around the back edge are less likely to damage the door, but they slide around if you're not careful.
Do not trust the weight capacity
The product pages all said "holds up to 20 pounds of laundry." That's a lie. I filled one fully with a week's worth of towels — 18 pounds. The hook held. The bag didn't. The stitching where the canvas meets the rings gave out in three places. The second one with a "heavy-duty steel frame" started sagging after a month. The bag itself was fine, but it swung so much every time I tossed a sock in that the hooks loosened. I tighten them every Sunday now.
The hallway test
I live in a 1930s apartment with narrow doors. Everything I test, I test in the hallway with a load of laundry in my arms. Most door hampers hang over the side, meaning you have to squeeze past them. The one that stayed put longest was the one with a flat back that hugged the door, not a rounded one that pushed into the hallway. It's the difference between brushing the fabric and knocking the whole thing off its hooks.
Who should skip the door hamper entirely
If you've got a family of four with a shared hallway that sees three people walking each morning, a door hamper becomes a tripping hazard on day one. The hook keeps bending. The bag sags into the walkway. You're better off with a laundry hamper that sits inside the closet or against the wall. Same goes for doors that aren't solid wood — a hollow core door can't take the weight without stress marks. I tried it once in my old apartment, and the door now has a permanent dent where the hook pressed.
For everyone else, a door hamper works, but only if you measure the gap, check the stitching, and buy one with a hook that doesn't flex. The one I kept is a basic canvas bag on a steel frame that says 15 pounds on the lid. I've loaded it heavier, and it's still hanging after nine weeks. Didn't need the rubber mallet either.
More on laundry setups: Best Laundry Hamper: I Tested 6 for a Month, Here's the One I'd Buy and Wall Hanging Laundry Hamper: If It Flops, It's the Hooks.