These unmovable surfaces are harsh on bare feet, and the thin rubber sole of many flip-flops does little to adequately absorb the shock they produce.

CNN: Flip-flops present feet with a painful problem

One new company, CitiSoles, started by two New York University students, Susie Levitt and Katie Shea, offers a new twist: A ballet flat with a rubber sole that splits in the center, making it easier to fold and tuck into a zippered pouch, which also unfurls into a tote for carrying high heels home at night.

FORBES: Magazine Article

Gambassi also developed a durable, sticky resin from a Para rubber tree plant, to bind the sole to the top of Brough's stiletto and platform heels.

FORBES: Fancy Footwork