Does humidity affect hydrophobic mousepad coatings?

Yes. Humidity accelerates the breakdown of siloxane or fluoropolymer coatings via hydrolysis, so in humid environments (>60% RH), the water-beading effect fades in about half the time compared to dry climates. Most coated mousepads aren’t designed for tropical conditions, so you’re better off with a Cordura or polyester pad, or just accepting more frequent replacements.