Novel aspects concerning the micromechanical response of amorphous regions confined by crystals in nano-sized domains are illustrated for semicrystalline poly (ethylene terephthalate)(PET), on the basis of microindentation hardness and dynamical mechanical spectroscopy (DMS) analyses (10-3÷ 60 Hz frequency range for DMS). PET samples were crystallized from the glassy state at low and high temperatures (T c= 100° C and 160° C, respectively) and subsequently recrystallized some degrees above to gain information on the nature of the amorphous regions. DMS at 95° C reveals two segmental relaxation processes ascribed to the interlamellar amorphous regions (slow mode) and to the interstack amorphous pockets (APs)(fast mode) respectively, the latter being the object of the present study. It is shown that recrystallization changes the cooperativity within the APs. At low T c, an increase in the …