Traditionally, cabinets were completed using unfinished wood in the interiors. In stock cabinetry options, this typically meant lower-quality plywood or even particle board on the bottoms. The wood was a little rough, unattractive and it was a catch-all for dirt and debris. So, back in the "old days" there was a right-of-passage performed by homemakers when they moved into a new kitchen; they lined cabinet shelves and drawers with shelf liners.