But a few designers are trying. They're offering shoes that can change - from high heel to low heel, from one size to a bigger size, from one outer skin to another - for better fashion, comfort or fit.

ADJUSTABLE HEELS. Camileon Heels developed a new kind of shoe last, or form, that allows the heel to go from 3 to 1 inches. Pull down on the heel, push it forward and tuck it under the arch of the shoe.

Since launching last year, Camileon has produced 50 styles, at prices from $225-$325, sold at specialty footwear retailers and online (CamileonHeels.com).

INTERCHANGEABLE "SKINS." Skins Footwear features a foot form called the Bone, which cradles the foot and slips inside soft, collapsible "skins," or outer shells. They're available at SportieLA.com (and at Zappos.com in mid-July), and in about 100 specialty retailers around the country by fall.

INTERCHANGEABLE THONGS. Switchflops are flip-flop sandals with Velcro-covered thongs that can be switched with different colored and patterned straps.

There are three styles ($32-$47) and 50 straps ($10 each), available at specialty boutiques and online (Switchflops.com).

ADJUSTABLE SIZING. Inchworm shoes, for children ages 3 to 9, "grow" with a child's foot. The shoes have a button and a bellows; push the button and the shoe expands in half-size increments up to a full size larger (for example, 10-10.5-11).

Sold mostly online at InchwormShoes.com, the shoes cost $79 a pair and come in more than 10 styles. - USA TODAY