Hair can absorb upto 40% of its own weight in water and once wet it can stretch by 40-50% of its dry length!
Hair is much more elastic and pliable when it's wet making it easier to manipulate and style. This is why it is easier to curl wet hair and then let it dry rather than curling dry hair.
That said, hair is actually at its strongest when it is dry (The Science of Black Hair by Audrey Davis-Sivasothy) so when you want to detangle hair it is better to work with damp hair rather than either very dry or very wet hair.
A smooth one with wide teeth like the one to the right. Click the image to get the stylish trio.