Recent results obtained by studies on the network properties using positron annihilation lifetime spectroscopy and swelling measurements in the ureasil-based and photocross-linked polymer matrices are compared. Common features observed are the larger difference (αF2 − αF1) of the coefficients for the thermal expansion of free-volume holes αF1, αF2 below and above Tg, respectively, in the polymer matrices, the highest sensitivity of the amperometric enzyme biosensors constructed based on the polymer matrices. It is suggested that the correlation found may be more general. It seems, therefore, that controlling the network properties of polymer matrices suitable for construction of amperometric enzyme biosensors by examining (αF2 − αF1) magnitude in temperature dependent positron annihilation lifetime spectroscopy experiment may be used for improvement of operational parameters of such sensors.