But Curin said researchers, who typically refer in their studies to cheap rubber flip-flops that can be purchased at discount stores, must realize not all flip-flops are created equally.

CNN: Flip-flops present feet with a painful problem

Carnival brights and vibrant prints are hot in home decoration, and humble Brazilian flip-flops - the rubber sandals worn by the country's president, supermodels and street kids alike - are set to be this summer's hottest shoes.

BBC: A replica of Rio's Christ the Redeemer in London's Oxford St

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

But the rubber soles of most flip-flops just bend all over the place, while the stiff soles of some stylish varieties may not bend at all, she said.

CNN: Flip-flops present feet with a painful problem