What Are Mattress Springs Made Of?

Mattress springs are metal coils, and most are made with tempered steel.

Tempered steel coils

Engineered Sleep describes its high-tensile, US-made steel coils as tempered for maximum “memory.”

• Tempering heats the wire or innerspring unit to a high temperature, either electrically or in an oven.
• Tempered innersprings are described as stronger and more durable.

Titanium spring sizing

A titanium spring may need more coils or a different wire diameter to achieve the same spring rate.

• When comparing designs meant to match a spring rate, check the coil count as well as the material.
• Check the wire diameter too, since a titanium spring may use a different size for the same rate.

One patent example forms a five-turn spring by coiling high-tensile carbon-steel wire.

1. The patent example uses 2.18 mm or 2.39 mm high-tensile carbon-steel wire.
2. A coiling machine forms a 5-turn spring from the wire in that example.

These are details of one patent example, not a specification for all mattress springs. If a mattress listing names the wire size or number of turns, treat those as separate build details; coil height and turns also shape firmness. Check the stated coil design rather than assuming those example dimensions apply to every mattress spring.

Tempering uses repeated heating and cooling to improve a coil’s resiliency.

• One maker says its springs bounce back to their original shape year after year without sagging.
• Tempering can be done electrically or in a tempering oven.
• If a listing says its coils are tempered, ask how the tempering was done and what it is meant to improve.
• One patent gives a range of 284 to 290°C for 10 to 14 minutes and also states approximately 287°C for approximately 12 minutes.
• Original Mattress Factory says a coil cannot be tempered twice after reaching its optimum tempering temperature.

When comparing a product claim about tempering, check whether the maker explains the process and what it says tempering is meant to do. The sources describe different methods and one patent’s specific time and temperature, so do not treat that patent example as a requirement for every mattress coil.

Bonnell, offset, and continuous-wire coils use different designs; the facts here describe an example or feature of each type.

Bonnell coils

One mattress maker uses a Bonnell coil unit in its Oasis line.

• Check whether a mattress listing names Bonnell coils; the Oasis example is specific to one maker’s line.
• Do not assume every mattress uses the same coil type just because it has a spring support unit.

Offset coils

Offset coils can flex like a hinge under lighter pressure, with stronger pushback under greater load.

• One mattress maker says its square-head design works with neighboring coils to hinge and conform to the body.
• Check whether a product describes a square-head design, which one maker says works with neighboring coils to hinge.

Continuous-wire coils

Continuous-wire coils are made from a single wire formed into rows of loose coils. Check whether the listing describes one wire formed into rows, rather than assuming that a high coil count identifies the design.

Small coils may appear in comfort or transitional layers, and the listed heights differ between microcoils and nanocoils.

Microcoil height

Tom’s Guide gives microcoils a height of 1 to 4 inches.

• Check the mattress listing for the stated microcoil height rather than assuming every small coil has the same size.
• Small coils can create more room for airflow in comfort layers.

Minicoil placement

Minicoils are often used in comfort or transitional layers, between comfort materials and the support core.

• Check the layer description to see whether minicoils sit between comfort materials and the support core.
• Look for whether the listing places the minicoils in a comfort layer or a transitional layer.

Nanocoil size

Tom’s Guide describes nanocoils as less than an inch tall.

• Compare the stated size with the 1 to 4 inch height range given for microcoils.
• If a listing calls its small coils nanocoils, check that the stated height is under an inch.

Some pocket coils have an individual fabric wrap; the wrap is separate from the steel spring itself.

Nonwoven polypropylene

One mattress maker identifies nonwoven polypropylene as the fabric around each of its pocket coils.

• The fabric wrap separates the coils so each can respond to pressure directly above it.
• Food-grade nonwoven polypropylene is used by Avocado for durability and to meet finished-product testing.
• When comparing pocket-coil mattresses, check the listed wrap fabric rather than assuming every mattress uses the same material.

Helical wires can join spring elements, while border wires or border coils may reinforce the perimeter.

Helical connecting wires

A patent describes helical wires securing spring elements together to form a unit of the desired size.

• Check whether the construction description says helical wires secure spring elements together.
• Distinguish row-joining wires from a perimeter border wire, which is a separate part in the patent example.

Perimeter border wires

One patent example bends two lengths of 4 mm border wire into two rectangles.

• Some innerspring units use a border rod around the perimeter for added edge support, according to a mattress maker.
• Avocado says firmer border coils run around the perimeter so the surface holds its shape from corner to corner.
• Check the specific mattress design; the examples describe different ways to reinforce an edge.

Materials above or around coils can include fabric, fiber pads, latex, and wool, depending on the mattress.

Insulator pads

An organic cotton fabric insulator sat above high-density microcoils in a mattress comparison described by Tom’s Guide.

• One hybrid mattress specification lists a 0.75-inch, 1.5-ounce fiber-pad support layer.
• Avocado describes a pad of dense natural fiber that stabilizes coil units and resists compression over time.
• Check the product’s layer list for the pad material and where it sits, since the examples describe different materials and constructions.

Foam and latex

One mattress maker describes organic latex and wool above its coil unit, with a microcoil layer in some plusher models.

• Polyurethane, memory, and high-resiliency foams in Engineered Sleep mattresses are described as CertiPUR-US certified.
• Latex is used instead of polyurethane foam in Avocado’s mattress materials approach.
• Check the materials list for the specific mattress; these examples do not describe one shared build.

Coil-wire gauge describes wire thickness, but gauge alone does not determine how firm a coil feels. Mattress coils are usually 13 to 17 gauge, and a lower gauge number means thicker wire. Lower-gauge coils are firmer and more durable, while higher-gauge coils are more flexible and responsive.

Coil height and number of turns also shape firmness, so compare more than gauge when reviewing a coil description. Continuous-wire coils can have a high coil count while using thinner wire and fewer turns, according to one mattress maker. If you want a firmer, longer-lasting coil, look for a lower gauge number in the listing, then check the coil height and turns before you decide. If you prefer a more flexible, responsive feel, a higher gauge number may suit you better.

A higher coil count alone does not directly prove that a mattress is sturdier or more durable.

• Coil count is simply the number of springs, and quality depends on how they are engineered together, one mattress maker says.
• Sleep Foundation lists several typical coil-count figures; compare a count with the coil type rather than reading it alone.
• Continuous coils can have a high count while using less steel and thinner wire, according to one mattress maker.
• A high count can be manipulated with pencil-thin coils around the sides, Pocket Spring Store warns.
• Pocket Spring Store says it uses coils of the same size and geometry.

When checking a listing, ask what the count includes and whether the coils across the sleeping surface share the same size and geometry. Use coil count alongside construction details, not as a stand-alone quality claim.

One seller describes its coils as made with recycled steel, and steel mattress springs can be recycled where services are available.

• Pocket Spring Store says its units are made with 98% recycled steel.
• Steel springs appear on Connecticut DEEP’s list of mattress components that can be recycled.
• Roughly three-quarters of mattress and box-spring components can be disassembled and recycled, according to Massachusetts.
• About 27.8% (4.7 million tons) of ferrous metals from durable goods, including furniture, were recycled in 2018, the EPA estimated; this is not a mattress-specific rate.
• Where mattress recycling is available, Avocado’s steel coils can be recovered and recycled.

If recycled content matters to you, check the specific claim for the mattress or coil unit. For disposal, check whether mattress recycling is available where you live.

How many turns should a mattress coil have?

A patent example uses a 5-turn spring, but coil height and turns both shape firmness.

Does every pocket-coil unit need a scrim sheet?

Not every design needs a top scrim sheet: a QuadCoil design says one is not necessary, while QuadMinis generally do not perform as well on other makers’ units unless those units include a scrim sheet.

Can steel coils rust when damp?

Yes, persistent dampness can invite rust in a coil mattress. One maker says its steel coils sit deep inside fabric pockets away from direct moisture, but that does not establish that damp steel cannot rust.

Are plastic bed springs mattress coils?

Conventional mattress coils are described as metal springs, while FLEXIMA describes a recyclable-plastic modular understructure that replaces traditional slatted frames. Check whether the plastic support system is part of the mattress or the bed base.

We read 17 published pages from 15 sites (Sleep Foundation, engineeredsleep.com, avocadogreenmattress.com, tomsguide.com and 11 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.