It is made of phosphated, carbon‑tempered steel wire with a diameter of 2.2 mm or 2.0 mm. The tempering process is essential, as it strengthens the steel and makes it resistant to deformation. This characteristic prevents the formation, over time, of annoying depressions on the mattress surface especially in high‑load areas caused by the gradual weakening of the spring system.

The assembly is achieved using a spiral steel wire that connects a series of springs in rows. The spring structure forms the load‑bearing support of the mattress and serves as an anchoring base for the padded layers.

The Bonnel spring system is the most traditional solution and can be produced with 450 or 650 springs (in the double‑size version), depending on the model used. The larger or smaller diameter of the end coils determines the number of springs required for the structure.
The Bonnel spring allows for the creation of both medium‑firm anatomical mattresses and high‑firmness orthopedic mattresses.