The present invention provides a bag filter comprising a melt-blown fibrous nonwoven web formed into a bag configuration with a closed end, an open end, an inside surface, and an outside surface. The bag filter is constructed such that (a) the fibrous nonwoven web comprises fibers such that 90% of the fibers have a diameter ranging from a minimum fiber diameter to a maximum fiber diameter which is no more than about three times the minimum fiber diameter, (b) the fibrous nonwoven web as oriented in the bag filter has a tensile strength in the circumferential direction at least about 1.5 times the tensile strength in the longitudinal direction, and/or (c) there is no side seam and an injection-molded thermoplastic elastomer end closure. The present invention also provides a method of treating a fluid by passing the fluid through such a bag filter.

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