This refers to the knowledge of the Rubber Duck Standard and the proper use of a rubber duck. A picture says more than a thousand words. Other ducks are not genuine rubber ducks, only inferior copies of the real thing. A rubber duck has to have good floating capabilities. It should always swim head up.
Rubber ducks are no soakers.
Unfortunately, rubber ducks are not made out of rubber, but plastics is a good substitute, if it is soft and regains its shape after deformation the way rubber does. A rubber duck may squeak. But it is not a required feature, only optional. A duck like this is superior. As rubberduck mannequin the rubber duck from kumiankka.cs.tut.fi by Panze Needless to say, a rubber duck should be used and treated properly.