I go through three sets of pads a season - they're obviously not too durable, and they don't absorb much moisture. On hot days these pads get saturated quickly. Since they're part of the fit and what keeps the helmet comfy, I keep replacing them. Get a sweat band if you want help managing perspiration.
I guess helmet pads are a necessary evil. I'm on my 3rd set this season. They delaminate the cloth peels off the padding. Maybe I have acid sweat. I keep them clean, but they just don't last.