The process of turning used products into new products is called recycling. It involves collecting discarded materials, sorting and cleaning them, and reprocessing them into raw materials or new objects. Paper can become new paper, glass can be melted and remade, and metals can often be recycled repeatedly without losing much quality.
Recycling is one part of the familiar “reduce, reuse, recycle” hierarchy. It differs from reuse, in which an item is used again largely in its existing form, and from composting, which biologically breaks down organic waste. Recycling may be mechanical, such as shredding and melting plastic, or chemical, such as breaking polymers into their component chemicals.
A common mix-up is assuming that every recyclable item is actually recycled. Contamination, mixed materials, poor local collection systems, and processing costs can prevent that. Some recycling is closed-loop, returning material to the same type of product; other recycling is open-loop, or downcycling, turning it into a different product of lower or altered quality. The term became especially prominent alongside modern waste-management systems during the 20th century.