microporous membranes are needed in order to hold back alcohol and water and permit water vapor to escape furthermore such a hydrophobic film is suitable for rainwear sport clothing gloves and shoes the membrane is not however limited to applications in which water vapor permeability is required and water is to be blocked by omitting hydrophobic or oleophobic additives which modify the surface tension of the membrane material the latter can be adapted to the particular requirements but the porous structure is retained in every case a common commercial polyester elastomer powder with a segmented polymer chain structure consisting of polybutyleneterephthalate hard segments and polytetramethylene ether soft segments with a shore d hardness of 40 a specific weight of 1 16 g cm 3 and a melting point of 168 u00b0 c is dissolved in dichloromethane the solution adjusted to 12 weight percent has a viscosity of 0 2 pa sup s measured with the brookfield rotating viscometer at 20 rpm with spindle no 2 to 93 parts by weight of deionized water 1 9 weight parts of a 40 common commercial ionomer dispersion of aliphatic crosslinking polyester urethane are added the particle size of the dispersion amounts to 0 1 to 0 4 microns after the addition of 2 0 weight parts of a 25 polyacrylic acid dispersion for thickening and 4 0 weight parts of concentration ammonia a brookfield viscosity of 0 14 pa sup s is established measured with spindle no 4 at 20 rpm 675 weight parts of the 12 polymer solution a are placed in the reactor with intensive stirring 325 weight parts of aqueous phase b are slowly added a w o emulsion forms having a viscosity of 5 5 pa sup s measured with the brookfield viscometer spindle no 4 at 20.