Recycling by product massive number of types of plastic, they each carry a resin identification code, and must be sorted before they can be recycled. This can be costly; while metals can be sorted using electromagnets, no such 'easy sorting' capability exists for plastics. In addition to this, while labels do not need to be removed from bottles for recycling, lids are often made from a different kind of non-recyclable plastic. To help in identifying the materials in various plastic items, resin identification code numbers 1-6 have been assigned to six common kinds of recyclable plastic resins, with the number 7 indicating any
Recycling symbol indicate that a product was "recyclable". The other two variants had the Möbius loop inside a circle—either white on black or black on white—and were meant for products "made of recycled materials", with the white-on-black version to be used for 100% recycled fiber, and the black-on-white version for products containing both recycled and unrecycled fiber. For example, a paper envelope might have both the first and last of these four symbols, to indicate that it was recyclable, and made from both recycled and unrecycled fibers. In addition to the resin identification codes 1–7 in the triangular recycling symbol, Unicode lists