[notauser]

Aluminium or Titanium frames make the best travel bikes.

- Unlike steel, they don't rust.

- Unlike carbon, they can cope with rough treatment (for example when loaded into the hold on a plane). They are less likely to be damaged, and the damage is more likely to lead to a gradual failure.

Titanium is reputed to be better but modern Aluminium frames are pretty light, pretty comfortable, and vastly cheaper.

I have an aluminium bike that I use whenever my trip involves a train ride or a flight.

[lokedhs]

I currently ride a titanium hardtail MTB. It's an amazing ride. I vastly prefer it over aluminium. Titanium has a reputation for being expensive, but that's only true because the famous brands have such high margin on them (no doubt to preserve that premium reputation).

[NathanielK]

Frame rust isn't a big deal on bicycle. Even in the 80's high-alloy steel like 4130 "Chromo" has been popular with bicycles. I've abused my 70's mtb bicycle with thousands of km of rustbelt winter riding and my frame shows no worrying corrosion, just surface discoloration where the paint has been scratched.

Carbon fiber is more durable than people give it credit for too, though because it's a brittle material that fails suddenly, larger safety factors should be used.