Individual Pocketed Springs: Each helical (hourglass-shaped) spring is housed in its own fabric pocket.

High-Grade Steel: The spring wire should be high-carbon, hardened, and tempered for superior resilience and

 long-term durability (resistance to sagging).

Quality Pocket Fabric: The fabric that houses each spring is crucial. Premium units use durable, non-woven

polypropylene or polyester fabrics that are breathable and resist moisture. Some may use knitted fabric for even

 greater flexibility.

Reinforced Borders: The perimeter of the unit should have reinforced springs or a foam encasement to provide

edge-to-edge support and prevent roll-off.

Zoning: A premium feature involves creating firmness zones within the unit (e.g., firmer springs in the hip and

 shoulder zones for ergonomic support). This is often a 3-zone, 5-zone, or even 7-zone system.