Speaker 101 - tweeter, cone material

Ceramic, silk, paper, polypropylene, polymer comoposite, aluminum, magnesium, kevlar, etc.
I realize that any one material for the tweeter or the cone is better than the rest the speaker selection would be a simple choice. I know it is not the case. There are many more factors involved in making a good speaker. However, each material must have its own strength, weekness and sound qualities. So can you tell me what they are? What is Kevlar?
I am just correcting my first sentence. I realize that if one ....is better than the rest, .............. I left out "if". Sorry for my poor sentence.
>> What is Kevlar?