A spring mattress, also known as an innerspring coil mattress, is made of a base layer of metal spring coils, topped with comfort layers made of soft material to cushion the sleeper from feeling the coils. It's considered A traditional mattress type and is currently the most commonly used mattress type in America. The feel of a spring-type depends on a variety of factors, including how many layers of coils it has, the coil gauge and shape, and how the coils are arranged. Some of the most popular types of innerspring mattresses include:  Bonnell coil mattress: Also known as open coils, Bonnell coils are individual hourglass-shaped coils. These are distributed evenly throughout the mattress and connected by metal wires. It’s the oldest and most traditional spring mattress, as well as the cheapest.
Offset coil mattress: Offset coils share the same hourglass shape and linked wires as Bonnell coils, but the convolutions of the individual coils are flattened at the top and bottom. The steel coils conform to the body and are more durable than Bonnell coils, but the links can result in more motion transfer.
Continuous coil mattress: Continuous coils are made of a single wire twisted into thousands of coils, using helical lacing to create a connected metal coil layer. Firm, stable, and durable, this type of innerspring mattress is relatively inexpensive, but its straightforward design makes it prone to motion transfer.
Pocketed coils mattress: A pocket coil spring mattress uses individual springs wrapped in fabric, making it a highly supportive mattress with good motion isolation compared to other spring types. However, pocket coil mattresses tend to be pricier.
Coil-on-coil mattress: This type of mattress uses layers of coils stacked together, reducing its springiness and giving more support.