corrugated

/ˌkɔrəˈgeɪdɪd/

Corrugated means molded into tight ridges and valleys. You've probably seen corrugated cardboard or corrugated metal roofs.

Materials are put into a corrugated shape to ensure elasticity and strength — cardboard boxes hold their shape because the cardboard is reinforced with a corrugated layer inside the two flat pieces. To remember corrugated, think about corduroy pants — which also have ridges and valleys. If you're lucky enough to have had ribbon candy, that's corrugated as well.

Definitions of corrugated

1. adjective

   shaped into alternating parallel grooves and ridges
   “the surface of the ocean was rippled and corrugated”

   synonyms:

   furrowed, rugged

   having long narrow shallow depressions (as grooves or wrinkles) in the surface