Abstract: A reseal member having a preferentially weakened central portion, and a method of its manufacture through the application of ultrasonic energy. The reseal is for use with an associated blunt cannula. The reseal comprises a central region and a peripheral region. The central region has a predetermined thickness and includes, in the direction of thickness, a weakened portion extending at least partially therethrough. The upper and lower surface portions of the reseal are continuous and unbroken. A method of forming the weakened central portion includes the steps of positioning the reseal member in an ultrasonic energy generating device, placing the member in compression, and imparting a predetermined amount of ultrasonic energy, in the form of vibrational energy, into the reseal member. The present reseal member can be used for solution vials and containers, tubing set Y-sites, and similar applications.