Both of our main cooling products - SOLAR CHILLtm and KAR KOOLtm - use a 6 or 8 inch thick fluted type pad as the wet cooling media, it is the most efficient evaporative cooling media in the world, and it should last for FIVE YEARS, WITH MINIMAL MAINTENANCE! (water quality is a factor) The Solar Chilltm coolers are now built of Stainless Steel (all wet parts), and the Kar Kools are sturdy plastic; neither will rust.