The reservoir is implanted under the groin muscles. A pump is also connected to the system and sits under the loose skin of the scrotal sac, between the testicles. Pumping transfers fluid from the reservoir to the cylinders in the penis, inflating them. Pressing on a deflation valve at the base of the pump returns the fluid to the reservoir, deflating the penis. When the penis is inflated, the three-piece inflatable prosthesis gives the penis stiffness and thickness similar to a natural erection.
Most men rate the erection as shorter than their normal erection, however.
When the prosthesis is deflated, the soft penis is somewhat fuller than an normal penis. The newest model the Ultrex, has cylinders that may increase in length, as well as in thickness and stiffness, with inflation. The ability of the Ultrex to lengthen the penis with erection varies with the health and elasticity of the tissue in the penis. Even with the Ultrex, most men will have erections that are somewhat shorter than they were originally. Despite men's concern about penis length, most women are not upset by this change.