Mattress density: what it is, how it is measured and which to choose
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In short
Mattress density is how many kilos one cubic metre of its foam weighs (kg/m³). It tells you how long the mattress will last, not how firm or soft it is. As a guide, for a support foam used every night by an adult, look for HR foam from around 30-35 kg/m³; memory foam usually sits between 40 and 60 kg/m³. And if you weigh more than 95 kg, rather than looking at a single figure, choose a mattress guaranteed for your weight: at Morfeo, that is the Morfeo XL mattress.
By Elena Fernández, Morfeo · mattresses made in Spain · updated 2 November 2026
In this guide
What mattress density is
Density is the amount of material in a given volume of foam. It is expressed in kilos per cubic metre (kg/m³): a 30 kg/m³ foam weighs 30 kilos per cubic metre. The more material there is in that volume, the more numerous and resilient the cells are, and the longer the foam takes to “tire”, that is, to lose height and keep the imprint of your body.
That is why density is, above all, an indicator of quality and durability. Two mattresses can feel the same on day one in the shop; the difference between a dense foam and a light one shows after two or three years, when the light one starts to sag around the hips.
How it is measured and how to find out a mattress’s density
In the factory, it is measured by weighing a foam sample of known volume and dividing the weight by the volume (the method set out in the EN ISO 845 standard for foams). At home there is no reliable way to work it out once the mattress is made, because it combines several layers and fabrics. What you can do:
- Look for it in the technical sheet. Reputable manufacturers state the density of each foam layer, not a single figure for the whole mattress.
- Ask layer by layer. “What is the density of the core and what is the density of the comfort layer?” If you are only given one figure, ask which layer it refers to.
- Be wary of “high density” without a figure. It is a sales phrase: what matters is the number and the type of foam (conventional, HR or memory foam).
- Check the weight it is guaranteed for. It proves the manufacturer has done the maths. At Morfeo we state it on every product page: up to 95 kg per person and, above that, the XL mattress.
Density is not firmness
This is the most common mix-up. Density tells you how much material there is; firmness tells you how hard it is to press into the surface, and it depends on the foam’s formulation, its thickness, the fabric and what lies underneath (springs, another foam). There are dense, soft foams, such as many memory foams, and light, hard foams that feel firm at first but soon give way.
So the right question is not “what density do I want?” but two others: what firmness suits the way I sleep? and is this foam made to last with my weight? For the first, see our guide on whether a firm or soft mattress is better; the second is the one density answers.
Typical density by foam type
No standard sets “the right density” for the whole market, but there are usual ranges that help you read a technical sheet:
| Foam type | Usual density | What it is used for | What to watch |
|---|---|---|---|
| Conventional foam (polyurethane) | Around 18-25 kg/m³ | Budget mattresses, guest beds, occasional use | Loses height sooner with daily use |
| HR foam (high resilience) | From around 30-35 kg/m³ | Support cores that recover their shape; youth mattresses and quality foam mattresses | That the figure is for the core, not a thin layer |
| Memory foam | Around 40-60 kg/m³ | Comfort layers that adapt to you and relieve shoulders and hips | Layer thickness and breathability |
| Latex | Measured differently; usually from 60 kg/m³ upwards | Elastic, adaptable comfort | That it is natural latex, if that is what you are after |
These are typical industry ranges, not a guarantee of quality on their own. A foam of good density badly combined (for example, a thick memory foam layer on a poor core) still makes a mattress that sags.
Which density to choose for your weight
Weight is what puts the most strain on foam, because it is concentrated at the hips and shoulders. This table sums up what to look for in a foam mattress and what we would recommend at Morfeo:
| Weight per person | In a foam mattress, look for | Morfeo recommendation |
|---|---|---|
| Children and teenagers | A high-density HR core; a light mattress that is easy to move | Juvenil Lite: high-density HR core and a perforated Visco Airscape® layer |
| Adults up to 95 kg | An HR core from around 30-35 kg/m³ or, better still, a pocket-spring core with a memory foam layer | Any mattress in the range; the most popular is the Original Hybrid |
| Over 95 kg | A reinforced structure and a guarantee for your weight; density alone is not enough | Morfeo XL mattress, designed for people over 95 kg |
| Couples with different weights | A mattress designed for the heavier partner | If one of you is over 95 kg, the XL; or two 90x200 mattresses suited to each of you |
A question we get a lot: “25 kg/m³ density, for how many kilos?”. It is a low density. It can do for occasional use or for a very light person, but for an adult sleeping on it every night it falls short: it will usually lose its shape sooner than you expect. If that is where you are, go straight for an HR core or a pocket-spring mattress. We explain this in more detail in our guide to the best mattress for heavier people.
If the mattress has springs, does density matter?
It does, but its role changes. In a hybrid mattress, support comes from the pocket springs, which each work independently and do not “tire” the way cheap foam does. Density then matters in the comfort layers on top: the memory foam or the foam that relieves pressure on shoulders and hips. A good combination is a spring core with a good-density memory foam layer, which is what the Original Hybrid has.
If you are torn between an all-foam mattress and a hybrid, this guide explains the difference between foam mattresses and hybrid memory foam mattresses, and here are the best hybrid mattresses.
What goes into each Morfeo mattress
Instead of giving you a single figure, we tell you what each one is made of, so you choose by the way you sleep and not by a number:
Original Hybrid
More than 2,000 pocketed micro-springs with a memory foam layer. High firmness with a soft feel on top and a removable cover washable at 30 °C.
Morfeo XL
Pocket springs and high-density foam in a reinforced structure, designed not to sag under heavy use.
Juvenil Lite
High-density HR core and 4 cm of perforated Visco Airscape®. 22 cm high and suitable for adjustable beds.
And three more for particular tastes: the VisCool, the coolest in the range, with soy-oil memory foam; the Altus, with the same micro-spring core as the Original Hybrid and a linen fabric; and the Nature, medium firmness, with natural latex and a built-in organic cotton topper. They are all in the Morfeo mattresses collection.
No small print
Trial, guarantee and delivery
- 100-night trial. No minimum number of nights: if you are not convinced, you can return it from day one and we collect it at our expense.
- 10-year guarantee on mattresses. It covers manufacturing defects.
- Free delivery to mainland Spain and mainland Portugal, in 3-7 working days in mainland Spain.
- Made in Spain, to order, in our factory in Yecla (Murcia).
All Morfeo mattresses arrive rolled in a box. It is ready to sleep on in 48 hours; if you can wait, 72 hours is ideal.
Frequently asked questions
What is the best density for a mattress?
There is no single figure: it depends on the type of foam and the layer. As a guide, for an HR foam core used every night by an adult, look for around 30-35 kg/m³ or more, and for a memory foam layer, between 40 and 60 kg/m³. If the mattress has pocket springs, the springs provide the support and density matters in the comfort layers.
How is mattress density measured?
A foam sample of known volume is weighed and the weight is divided by the volume; the result is given in kg/m³. You cannot work it out at home once the mattress is made, so the reliable source is the technical sheet, with the density of each layer.
25 kg/m³ density, for how many kilos?
It is a low density, typical of conventional foams. It can do for occasional use or for a very light person, but for an adult sleeping on it every night it falls short and usually loses its shape early.
Does higher density mean a firmer mattress?
No. Density tells you how much material there is and how long it will last; firmness depends on the formulation, the thickness and what lies underneath. There are dense, soft foams, such as memory foam, and light foams that feel hard but soon give way.
What density should a memory foam mattress have?
The memory foam layer is usually between 40 and 60 kg/m³. What lies beneath matters just as much: good memory foam on a poor core ends up sagging. That is why at Morfeo we combine it with pocket springs, as in the Original Hybrid and the VisCool.
I weigh over 95 kg: what density do I need?
More than a specific density, you need a mattress with a reinforced structure that is guaranteed for your weight. At Morfeo, all mattresses are guaranteed up to 95 kg per person; above that, the right model is the Morfeo XL mattress, with pocket springs and high-density foam, designed for people over 95 kg.
Still unsure which model to pick?
Try your mattress for 100 nights at home. If you are not convinced, we collect it free of charge.
