| abstract |
Filter media, such as electret-containing filter media for filtering gas streams (eg, air), are described herein. In some embodiments, the filter media can be designed to have desirable characteristics, such as stable filtration efficiency over the life of the filter media, increased normalized gamma, relatively low pressure drop (ie, resistance), and/or Relatively low set weight. In certain embodiments, the filter media can be a composite of two or more types of fibrous layers, wherein each layer can be designed to enhance its function without substantially negatively affecting the performance of the other layer of the media . For example, one layer of the media can be designed to have a relatively low basis weight and/or a relatively high air permeability, and another layer of the media can be designed to have a stable filtration efficiency and/or over the life of the filter media relatively high efficiency. |