The aluminum line of Rimowa models have a good overlapping flange to seal out sand, dirt, dust, and water.

They are not submarines as a Pelikan case is, if that is what you need. I can vouch for Rimowa alu cases keeping our packed contents clean and dry from torrential downpours in Brasil ( Fortaleza, Belem, Manaus (daily), and Salvador). Rome too, which receives as much rain as London. Never a problem.

But the Salsa cases do an equally good job on weather protection. We returned from a good trip to Brasil without problems using Salsa Lite carry-on and Salsa checked baggage. The zippers work very well. Scuffs, and some marks but nothing inside wet, dusty, damaged, or stolen. I have some concerns about the round corner protection longevity on one of our checked cases, but you cannot match how lightweight and easy it is to move in the airport between terminals with the Salsa line. A noticeable ease of movement and exertion, especially enhanced with 4 wheels per case.

Poly cases are quite light in construction to start with, a real plus with building your desired pack items around an airline weight limit. Despite the annual Christmas gift tonnage, we haven't found that we had to leave anything behind: The bills can wait, of course.