Microporous material exhibiting increased whiteness retention

In microporous material which on a coating-free, printing ink-free, and impregnant-free basis comprises:

• (a) a matrix consisting essentially of substantially water insoluble thermoplastic organic polymer,
• (b) finely divided substantially water-insoluble filler particles, of which at least 50 percent by weight are siliceous particles, said filler particles being distributed throughout said matrix and constituting from 40 to 90 percent by weight of said microporous material, and
• (c) a network of interconnecting pores communicating substantially throughout said microporous material, said pores constituting from 35 to 95 percent by volume of said microporous material,
• the improvement wherein said microporous material comprises whiteness retaining organic surface active agent selected from the group consisting of N,N-bis(2-hydroxyethyl)cocoamide, octyl-dimethyl-2-hydroxyethyl quaternary ammonium methane sulfonate, octyl-dimethyl-2-hydroxyethyl quaternary ammonium dodecylbenzene sulfonate, sofa dimethyl ethyl ammonium ethosulfate, polyethyleneglycol (400) monolaurate, stearamidopropyldimethyl-2-hydroxyethylammonium nitrate, dimethyl cocobenzalkonium chloride, and lauramine oxide.