There are several types of ballet tutu:
Romantic Tutu: three quarter length bell shaped skirt made of tulle. The hemline falls between the knee and the ankle. The romantic tutu is free flowing to emphasise lightness, to suit the ethereal quality of the romantic ballets such as Giselle or Les Sylphides. It is said to have been invented, or at least popularized, by Marie Taglioni.
Classical Tutu (bell): A very short, stiff skirt made with layers of netting with a slight bell shape and fitted bodice. It extends outwards from the hips and does not use a wired hoop. It is usually longer than a classical (pancake) tutu. These can be seen in the famous ballet paintings by Degas.
Classical Tutu (pancake): A very short, stiff skirt made with layers of netting that extends straight outwards (from the hips) in a flat pancake shape, and has a fitted bodice. The pancake style has more layers of net and usually uses a wire hoop and much hand tacking to keep the layers flat and stiff.
Balanchine/Karinska Tutu: also known as the "powder puff" is a very short skirt with no hoops, and fewer layers of netting than the pancake or classical styles. The skirt is loosely tacked to give a softer, fuller appearance. This style was designed originally for the ballet version of Georges Bizet's Symphony in C.
Platter Tutu: A tutu with a flat top that sticks straight out from the ballerina's waistline.
According to TutusChic, this is a nylon petticoat not a tutu, a lot of people confuse them with ballet tutus.
Tutus are usually made from the following materials:
Images from: WEHEARTIT