Wood absorbs water, so it is more efficient at cooling

Two-stage evaporative coolers do not produce humidity levels as high as that produced by traditional swamp coolers. In the second stage, the air passes through Boiler feed pumps Manufacturers water-soaked pads where it picks up humidity..

To cool the air, the fan in the swamp cooler brings air from outside through vents in the sides through damp pads. Direct Evaporative (Open Circuit) Cooling is used to lower the temperature of air by using latent heat of evaporation. Because the air is already cooled, it picks up less humidity than warmer air.

This is the most generic swamp cooler and is what is usually found on residential homes. The energy in the air does not change. Wood absorbs water, so it is more efficient at cooling passing air than some synthetic materials. The cooled moist air never comes in direct contact with the conditioned environment.

Lately, more modern materials, such as plastics and melamine paper are being used in cooler pads. The thickness of the pads plays a big part in the cooling efficiency.