Leather sandals get better wet. Suede does not.
Vegetable-tanned leather takes water and comes back darker and softer. Here is how to tell what you are holding, and what to do the first time it rains.

Vegetable-tanned leather is tanned with bark rather than chromium. It starts pale, it darkens with use, and it takes a soaking better than most people expect.
If they get wet, let them dry away from heat. A radiator will cook the fibre and crack it; a shaded floor will not. They will come back a shade darker and slightly softer, and that is the material working, not failing.
Suede is the same hide with the surface broken open, and water goes into it rather than over it. If yours are suede, keep them dry and brush them when they are.
One conditioner, twice a year, is enough for either. More than that and you are just filling the pores.
A short list, chosen slowly. Ten things we would own ourselves.
Once a month, at most
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