Whenever I need to travel with a clothes hanger, I use this awful plastic thing:
Beyond the fact that it’s flat and that the hook folds down, there really isn’t much design effort making this a travel-friendly item. With its broad outline it’s awkward to pack, and I’m always worried the thing is going to snap if weight is placed across it.
I don’t need a travel hanger often enough to seek out a good one, but I just came across this clever design, the Y002 by Japanese design brand Y:
Just a piece of leather and two pieces of wood. Thin enough to slip into a bag while hardly taking up any space. An almost-perfect choice of materials. I say “almost” because the designers do acknowledge one flaw, translated from Japanese here: “Since we are using real leather, if you use wet or humid clothing, or when used in a humid place, leather dyes may be transferred to clothing.”
The katakana in that last photo indicates the two wood options: Mahogany up top, and the lower one is made from Ramin, a tropical hardwood found in Southeast Asia.