PU or Poly-Urethane.
Poly-Urethane is Synthetic (plastic) material with minute bubbles or cells and a skin like surface. Used for upper materials, and in a different form for midsoles or padding foam. PU (upper material PU (short for polyurethane) upper materials usually use a thin layer of PU foam with a non-woven or fabric backing for reinforcement and strength. PU can come in thousands of different colors and textures.