The density of rubber would only be a factor if it was solid, not hollow, and then it'd depend on what kind of rubber. Most rubber is in fact more dense than water (per googling density of rubber).
The fact that it squeaks when squeezed, as well as common knowledge about bath ducks, tells you it's hollow, therefore the density of the material it is made of would be the wrong way to determine it it would float. It's the average density of the entire duck that matters (i.e. weight of duck vs weight of water displaced by duck's volume).
The fact that it squeaks when squeezed, as well as common knowledge about bath ducks, tells you it's hollow, therefore the density of the material it is made of would be the wrong way to determine it it would float. It's the average density of the entire duck that matters (i.e. weight of duck vs weight of water displaced by duck's volume).