Another utility knife often used for cutting open boxes consists of a simple sleeve around a rectangular handle into which single-edge utility blades can be inserted. The sleeve slides up and down on the handle, holding the blade in place during use and covering the blade when not in use. The blade holder may either retract or fold into the handle, much like a folding-blade pocketknife. The blade holder is designed to expose just enough edge to cut through one layer of corrugated fibreboard, to minimize chances of damaging contents of cardboard boxes.