Poly (vinyl alcohol) (PVA), is the largest synthetic water-soluble polymer produced in the world based on volume. It is produced commercially by the hydrolysis of poly (vinyl acetate) (PVAc) [1]. PVA has high enough tensile strength and satisfactory flexibility. To improve mechanical and other properties PVA is blended with different synthetic polymers [2]. PVA and PVAc composite films were prepared by casting two-component water-based system blends: a solution of the rigid PVA and emulsion of compliant plasticized PVAc [3, 4]. Natural fillers - monmorillonite clay (MMT) and microcrystalline cellulose (MCC) were added to PVA/PVAc blends. Diethylene glycol (DEG) is chosen as a plasticizer. Due to the fact that PVA is especially hydrophilic, and also considering the hydrophilic nature of one of the filler, much attention was paid to the water adsorption ability of composites as well as to the dependence of their strength-deformation characteristics, in particular modulus of elasticity, on the moisture content. Effect of adsorbed water content on elastic characteristics of films was evaluated at with relative humidity of 65% and 75%. Storage time in each case was determined by achieving constant moisture content. Elastic properties of films were identified by using thin-walled cylindrical specimens (TWCS Method). It can be assumed that in some cases a certain amount of water is involved in the formation of hydrogen bonds between the components, containing hydrophilic groups, which will increase the modulus of elasticity. On the other hand, water is a plasticizer for the PVA, thereby increasing the amount of water in the system will lead to a reduction in modulus of elasticity. To conduct an experiment at higher humidity (more than 75%) is not possible because the films with high content of water become very soft and lose their shape. At low humidity (below 65%) for a long time is necessary to achieve a constant water content which is very time consuming. Consequently, the value of the module of elasticity and the amount of adsorbed moisture is modulated using mathematical models obtained from data of experiments. In the present investigation a penalty function method with random search is used. The last stage is verification experiments in the point of optimal solution.