Innerspring
Innerspring mattresses are built with wire coils as the support structure. An innerspring mattress has a strong border wire attached to the perimeter of the coils to support the coils and help retain shape and reduce sagging. The edge on some models is reinforced with specially shaped springs or foam to support the sleep surface right to the edge, which helps prevent 'rollout' and edge breakdown. The upholstery is separated from the innerspring system by an insulator, a tough padding, wire or netting layer that prevents the upholstery from sinking into the coils.
