Extend your filter life: To get the optimum product life from your Phresh Filter, it should be used with the provided pre-filter sock. This pre-filter sock catches the large dust particulates and foreign materials which if allowed to come in contact with the carbon will ultimately clog the outer surface of the carbon before total internal saturation has been achieved. When this happens it unnecessarily shortens the product life of the filter. It is recommended that the pre-filter be machine-washed or replaced every six months. Extremely dusty environments may require a more regular cleaning program. Ideally, maximum air temperatures should be kept below 95 F (35 C). Relative humidity should be kept below 75% at all times. Remember, carbon will absorb moisture and will take up "space" in the carbon particulate, reducing its life span.