What is a bed spring?

Mattress springs are metal coils arranged to support a sleeper’s weight. Comfort layers cushion the body and buffer the sleeper from the core.

Bonnell coils are fairly firm.

Bonnell

• Bonnell coils connect to neighboring coils through helical wires.
• Each Bonnell coil is knotted at the end.
• Bonnell coils generally have reliable edge support.
• Compare the price if cost matters; Bonnell coils are among the least expensive mattress coil types.

Microcoils, minicoils, and nanocoils most often sit in comfort or transitional layers rather than the main support core.

• Support-core coils can be up to 10 inches thick.
• Small coils respond more immediately to pressure and form a deep cradle for pressure relief and support.
• Minicoils and nanocoils may be used with foam or latex support cores and are most commonly found in innerspring and hybrid beds.

Coil gauge measures wire thickness; compare other build details rather than relying on gauge alone. Mattress coils are usually 13 to 17 gauge; 13 gauge is thicker and 17 gauge is thinner. Wire diameter, coil diameter, turns, and preload all affect coil firmness.

A high coil count alone does not prove durability.

• Bonnell and offset coils are larger and tend to have lower counts than pocketed coils, which use multiple smaller springs.
• For a queen mattress, counts above roughly 1,500 to 2,000 often indicate extra spring layers, such as micro springs.
• A foam perimeter can remove rows of springs, reducing spring count and sleeping area in that mattress.
• Compare coil type and perimeter when interpreting the count.

Innerspring and hybrid mattress cores rely on steel springs that flex to absorb pressure as a sleeper moves. Core materials largely determine whether a mattress is categorized as innerspring, hybrid, foam, latex, or airbed.

A hybrid typically pairs pocket coils with buffer materials such as foam, latex, memory foam, gel-infused materials, or wool. An innerspring commonly uses Bonnell, offset, or continuous coils covered by comfort materials such as foam, wool, or fiberfill.

Sleeptronic describes a hybrid as all-foam construction coupled with a spring base, pairing spring responsiveness with foam cradling and pressure relief.

Comfort layers are meant to cradle and support the body; small, flexible coils can provide pressure relief and spinal support. For an open-coil mattress, check the upholstery layers; its comfort relies almost entirely on those layers.

Pocket coils can respond to movement without transferring motion to the surrounding coils. Innerspring support cores can use fabric-wrapped pocket coils to reduce noise, so check whether the coils are wrapped.

Most coil support cores let air travel freely and tend to regulate temperature well. If airflow matters, look for a coil support core.

Tempur-Pedic says its foundations provide a solid base rather than a box spring’s flexible give, and recommends considering the base because improper support can void the warranty. For Tuft & Needle mattresses, check slat gaps under 5 inches; wider gaps may let the mattress sink through and feel saggy.

Tuft & Needle says unevenness or sagging can occur when a frame or foundation does not support a mattress properly, so check the bed base as well as the mattress.

Are pocket coils also called Marshall coils?

Harrison Spinks credits James Marshall with inventing the first pocket-spring mattress, but that history does not establish whether “Marshall coils” is another name for pocket coils; check the mattress listing for its coil type.

Can a mattress use more than one coil layer?

The available information does not establish whether a mattress can use more than one coil layer, so check the model’s construction details. Sleeptronic lists more than 1,600 nano-coils in one queen-size mattress, but that count does not state how many layers it has.

Where can you find coil specs?

Avocado’s specification guide gives coil counts and innerspring specs by model and size.

Can mattress springs make noise?

Fabric-wrapped pocket coils in innerspring support cores can reduce noise.

We read 14 published pages from 9 sites (Sleep Foundation, tuck.com, tmasc.ca, help.avocadogreenmattress.com and 5 more), checked in October 2026. Every sentence in the answers above cites one of them; the offer card at the end names its own source. This page reports published sources only; we did not test mattresses in person.