Uncle Al wrote:

(snip)
Rain-X takes the opposite tack. Now R is a silicone oligomer and the
treated surface is hyperhydrophobic. Water violently beads but a
breeze blows it off. Very nice for windshields - your wipers glide
across the surface if you need them at all. After treatment, lightly
burnish the surface, wipe with rubbing alcohol, and burnish again.
That gets rid of most of the residual goo.

One wonders why competition swimmers don't "condition" their skin with
hydrophobes. Uncoupling the otherwise wetted surface would
substantially decrease friction.

Now that everybody knows, we should expect pre-competition exams by
forensic dermatologists at Olympic swim meets.