This invention relates to a a one-step process for making a polymer composite suspension for coating plastic films characterized in that a first polymer is synthesized in-situ optionally in the presence of other polymers and in the presence of clay. Preferably the polymer composite suspension comprises a) 1.0 to 11.0 wt % of clay or silane modified clay, b) 0.1 to 10.0 wt % of poly (acrylic acid), which is a copolymer of acrylic acid (AA) with at least one other monomer selected from 2-ethylhexyl acrylate (EHA), β-carboxyethyl acrylate (β-CEA), methacrylamidoethyl ethylene urea (WAM II) and ethoxylated behenyl methacrylate (β-EM), c) 1.0 to 15.0 wt % of other polymers, preferably poly (vinyl alcohol) and d) 70 to 97 wt % of water or mixture of water with 2-propanol. The coating films made from the suspensions show good barrier capabilities against water vapor and oxygen can be used to make barrier layers on or within plastic films for packaging applications. The invention also relates to methods for making silane modified clay usable in the process for making the suspensions.