Under the scope of this investigation, several characteristic features of the poly(ethtlene terephtalate) PET based systems are revealed. It is demonstrated that with increase of PET content, hardness, indentation modulus as well as tensile strength and modulus are substantially increased. Superelasticity of the investigated multiphase composites, in its turn, increase by increasing the concentration of low-modulus component. The effect of radiation modification on the properties of the investigated systems is strongly dependant on the composition of the blends. It is also shown, that there is strong correlation between morphology, structural properties (density, crystallinity, content of the voids) and micro and macro stress-strain properties of the investigated systems. Consequently, one can conclude that certain stress-strain properties of the investigated multifunctional systems can be predicted by means of mathematical models based on the morphology.