Over the past fifty years polymeric materials have found an increasing number of applications in several engineering fields. These include structural applications, use in advanced industrial processes and design of innovative devices. One of the most important polymer properties in several technological applications is mass transport of small molecules. Gas mixtures separation, composite materials` environmental resistance, adsorption devices, controlled release of drugs, high barrier flexible packaging are some examples. In fact understanding and characterization of mass transport and of thermodynamics of interaction between polymeric material and low molecular weight penetrants as well as knowledge of their relationship with polymer structure and morphology is of primary importance for these technological applications. In this paper we focus our attention on the optimization of polymers` mass transport performances and present three significant examples: analysis of advanced thermoplastic matrix composite materials` durability, optimal design of controlled delivery of drugs by means of monolithic devices based on water soluble polymers and development of biodegradable superabsorbing materials.