Do penile implants feel unnatural to women, or are they designed to be undetectable?

Somewhat natural: Penile implants are performed in order to have an adequate erection for sexual intercourse. There are 2 main types of implants, inflatable prostheses and malleable (rigid). The more natural implant is the inflatable prosthesis but it is definitely not undetectable. It is a plastic implant and can be felt within the penis during the flaccid state. These implants are not meant to be undetectable.

See below : The great majority of women can not delineate any difference between a natural erection vs that of a prosthesis with vaginal penetration. Regarding the sexual experience as a whole, in one study, women in the inflatable prosthesis group were more satisfied with the quality of their sexual relations and with their partner's prosthesis than were the women in the noninflatable prosthesis group.