What’s Inside a Mattress?

Understanding what’s inside a mattress is essential to choosing the right one for you. Every mattress is made up of several carefully designed layers. No matter what style or brand you pick, every mattress has three main parts:

• A support layer
• A comfort layer
• A sleep surface

These sections all work together to create the perfect sleeping environment, tailored to your body and sleep style.

I’m Hannah Shore, Head of Sleep Science at Mattress Online, and I’m going to walk you through each layer so you know exactly what you’re sleeping on — and how it helps your body recover while you rest.

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The support layer

The support layer forms the foundation of your mattress and plays a crucial role in maintaining proper spinal alignment while you sleep. 

During the day, activities like standing, carrying heavy bags, or slouching over a desk put strain on your spine. At night, our bodies experience atonia - a natural loss of muscle tone, which means we lose control over our posture while we rest.  That makes having the right support layer even more important, as it needs to support your body enough to allow your spine and muscles to relax and recover properly.

With the right level of support, your spinal discs can rehydrate, your muscles can truly rest, and recovery can take place, helping you wake up refreshed.

Sitting at the base of the mattress, the support layer provides essential structure for all the layers above it.

There are a few common materials used for this layer:

Springs

Traditional mattresses often use steel springs for long-lasting support.

There are several types of spring systems, with the three most common being:

1. Bonnell springs

Typically found in entry-level mattresses or children's beds, these interconnected springs offer a uniform level of support across the mattress.

2. Continuous coils

Made from a single continuous wire running the length of the mattress, continuous coils usually contain more springs than Bonnell systems, providing higher levels of support.

3. Pocket springs

Each spring is individually wrapped in its own fabric pocket, allowing it to move independently, much like piano keys. This design offers more tailored support and helps minimise partner disturbance. Full-height pocket springs provide the main support, while smaller ‘mini’ pocket springs can serve different functions within the mattress.

Foam

Another common option for mattress support is a solid block of high-density foam, often called reflex foam. Unlike the softer foams used in comfort layers, supportive foams create a solid and stable base. 

Foam support layers are practical, especially for rolled mattresses, making them easier to transport and set up at home. However, foam can retain heat and may soften over time, which can gradually alter the level of support your mattress provides.

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The comfort layer

Moving up from the base, the comfort layer is an essential part of what’s inside a mattress. This layer shapes how your mattress feels and plays a key role in regulating temperature, responding to pressure points, and matching your sleep preferences.

The materials used in the comfort layer each have their own benefits and potential downsides, so understanding them will help you find the best fit for your sleep needs.

There are three main types of materials you’ll commonly find in comfort layers:

1. Fibres

Materials like polyester or natural fibres are breathable and excellent at regulating temperature, helping keep you cooler throughout the night. However, they do tend to settle over time, leading to visible impressions where you sleep, much like how sofa cushions need regular plumping. Fibre-filled mattresses tend to feel a bit firmer than foam comfort layers.

2. Foams

Performance foams, such as memory foam and gel-infused foam, are designed to disperse pressure and reduce the risk of numbness or pins and needles while you sleep. These foams often feel softer but can trap heat and moisture, even when engineered to improve breathability.

3. Mini springs

Mini springs are smaller versions of the pocket springs used in the support layer. When combined with fibres or foams, they improve breathability and add a bit of bounce to your mattress. It’s worth noting that some manufacturers include these mini springs in their total spring count, but not all springs inside a mattress provide structural support; some exist purely for your comfort.

Different mattress types offer varying benefits based on their comfort materials. You’ll find options like:

• Memory foam mattresses
• Latex mattresses
• Gel-infused foam mattresses
• Natural mattresses filled with cotton, wool, or silk
• Eco-friendly white fibre mattresses. 

Each material brings unique properties, whether you’re seeking breathability, softness, bounce, or durability, to suit your personal sleep needs.

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The sleep surface

The outermost layer of a mattress is its cover - the wrap that protects all of the internal layers. Mattress covers are typically made from durable materials like polyester, viscose, or cotton, which are crafted into either knitted fabrics or damask.

• Knitted covers have a looser weave, making them softer, stretchier, and more breathable
• Damask covers are made from a tightly woven, smooth, and durable fabric that often features a subtle woven pattern, giving the mattress a refined look and feel.

Mattress covers can offer extra benefits depending on the materials used. For example, some covers are woven with copper or carbon fibres for their cooling and antimicrobial properties. Others might be treated to reduce allergies and repel dust mites, helping to keep your sleep environment healthier.

The finishing touches on a mattress cover also affect how it feels overall:

• Quilting and microquilting - this adds a plush, patterned surface on top of the comfort layers, creating a luxurious feel.
• Flat finishes - Common on rolled mattresses, flat covers skip quilting or tufting, for a sleek, simple surface.
• Tufting - This technique secures the mattress fillings firmly in place, providing a firmer feel and enhancing durability in fibre mattresses.

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Now that you know what’s inside a mattress, you’re one step closer to finding the perfect match for your sleep needs!

If you’re ready to learn more about specific mattress types, our Advice Centre is packed with expert guidance to help you make the right choice.

Or, our mattress firmness guide is a great place to start, while understanding the best mattress for your sleeping position can inform you of the mattresses best suited for your sleep.