Bath fan duct

There are 3 types of metal sheets (that you roll into duct) available at Home Depot

1) very thin aluminum
2) galvanized
3) thicker galvanized

I chose #2. But then the Home Depot guy said I should have chosen #1. He said aluminum does not rust, galvanized duct will RUST...

Is that true ???

Yes, steel can eventually rust when the galvanized treatment on its surface is somehow compromised. Hence, and especially in a damp application, the aluminum duct will outlast the galvanized-steel duct. Steel is better in a high-temperature application such as the venting for a gas furnace or water heater, but aluminum is preferable for damp applications such as dryer and bathroom vents.