A method for preparing a woven or nonwoven web comprising the steps of: (i) providing a raw woven or nonwoven web, wherein the woven or nonwoven web has a first and a second major surface and wherein the woven or nonwoven web comprises fibers comprising one or more polymers selected from the group consisting of polyarylene sulfides, polyolefins, polyamide imides, polysulfones, polyethersulfones, polyetherketones, polyether etherketones or copolymers thereof; (ii) contacting at least part of the woven or nonwoven web with a first solution of a salt of barium, strontium, calcium, lead or a mixture thereof; (iii) contacting at least part of the woven or nonwoven web with a second solution of a sulfate salt, sulfuric acid or a mixture thereof or with a gas or gas mixture comprising sulfur trioxide; and (iv) allowing the first solution and the second solution or the gas or gas mixture to come into contact, so that one or more inorganic salts selected from the group consisting of barium sulfate, strontium sulfate, calcium sulfate, lead sulfate or mixtures thereof are formed on the surface of at least part of the fibers, wherein the woven or nonwoven web comprises: fibers comprising one or more polymers selected from the group consisting of polyarylene sulfides, polyolefins, polyamide imides, polysulfones, polyethersulfones, polyetherketones, polyether etherketones or copolymers thereof; and one or more inorganic salts selected from the group consisting of barium sulfate, strontium sulfate, calcium sulfate, lead sulfate or mixtures thereof; wherein the one or more inorganic salts are present on the surface of at least part of the fibers. (i) providing a raw woven or nonwoven web, wherein the woven or nonwoven web has a first and a second major surface and wherein the woven or nonwoven web comprises fibers comprising one or more polymers selected from the group consisting of polyarylene sulfides, polyolefins, polyamide imides, polysulfones, polyethersulfones, polyetherketones, polyether etherketones or copolymers thereof; (ii) contacting at least part of the woven or nonwoven web with a first solution of a salt of barium, strontium, calcium, lead or a mixture thereof; (iii) contacting at least part of the woven or nonwoven web with a second solution of a sulfate salt, sulfuric acid or a mixture thereof or with a gas or gas mixture comprising sulfur trioxide; and (iv) allowing the first solution and the second solution or the gas or gas mixture to come into contact, so that one or more inorganic salts selected from the group consisting of barium sulfate, strontium sulfate, calcium sulfate, lead sulfate or mixtures thereof are formed on the surface of at least part of the fibers, fibers comprising one or more polymers selected from the group consisting of polyarylene sulfides, polyolefins, polyamide imides, polysulfones, polyethersulfones, polyetherketones, polyether etherketones or copolymers thereof; and one or more inorganic salts selected from the group consisting of barium sulfate, strontium sulfate, calcium sulfate, lead sulfate or mixtures thereof; wherein the one or more inorganic salts are present on the surface of at least part of the fibers.