Info from Riedell:
We have a variety of heels on high top models.
The basic PVC heel is built in to the rest of the sole. It is inexpensive and durable, but heavy.
Stacked leather heels are lighter than PVC, and also very durable. These are on more premium sets.
Our most premium heels feature stacked leather and cork. The cork is the lightest material, and has the best shock absorbing properties of the three.
The leather and leather/cork heels have a cap of hard rubber material on the bottom for added durability.
All three are good for skate parks because of high durability. Skaters who are doing inverts or flips and landing on heels a lot may appreciate the cork because of its shock absorbing property.
Robus is a mixture of ground leather and adhesive filler so is better than a PVC heel but doesn’t have enough leather in it to be called a leather heel