an infant formula mixer with a stem , with a region either proximal or distally which expands into a mixing membrane . the mixing cup like flexible and resilient membrane is applied at the bottom of its stem , and can be either pressure fitted , snap applied , or integrally molded , or even threadedly engaged , with the membrane , in its formation . such a membrane may be made of any polymer , acrylic , flexible rubber , or silicone . in typical usage of the mixer , it is applied in an up and down motion , at the distal aspect of the vessel , for such time as the clumps of formula are fractured and dissolved , and inherently mixed within the liquid within the container or bottle , in preparation for usage .