How to Compare Mattress Specs Like Density, ILD and Coil Types
September 9, 2026
Mattress specs rarely compare cleanly across brands, and many figures are never published at all. Use density, ILD and coil details to understand how a mattress is built and what to ask. Then let a lie-down test decide.
Table of Contents
- Why the Numbers Don't Line Up Across Brands
- Foam Density: How Much Foam, Not How Firm
- What ILD Measures, and Why One Number Isn't the Feel
- Coil Types, Gauge and Count
- Do Higher Numbers Mean Better or Longer-Lasting?
- The Lie-Down Test That Compares What Numbers Can't
- Your Spec Sheet to Take Along
| Spec | What it measures | What it can tell you | What it can't tell you |
|---|---|---|---|
| Foam density | Weight of a set volume of foam | How much material is packed in; a clue to shape retention | How firm it feels or how long it lasts |
| ILD (also called IFD) | Force to press a set distance into a foam sample | How firm that one sample is | How the whole mattress feels, or its quality |
| Coil type | How the springs are shaped and joined | Whether the unit moves as one or point by point | Firmness or lifespan on its own |
| Coil gauge | Wire thickness (lower number, thicker wire) | Which spring is stiffer, all else equal | Whether the mattress is better |
| Coil count | Number of coils in the unit | Something, but only against the same size and type | Support or quality across sizes and types |
Why the Numbers Don't Line Up Across Brands
Each figure measures one part of one mattress, tested one maker's way. Five things get in the way of a straight comparison:
Many figures aren't listed
Some mattresses at Mancini's Sleepworld list a coil count or a wire gauge, and many coil mattresses list individually wrapped (pocketed) coils. Foam is more often described in words such as "high-density" than with a density figure, and an ILD figure is rarely, if ever, given. When a figure isn't listed, ask.
Test data can be private
A peer-reviewed foam study notes that makers' detailed test data may be commercially sensitive and therefore difficult to access, so a missing figure isn't proof of a poor mattress.
The same test can be run several ways
The international indentation standard, ISO 2439, lists methods that press to different depths and hold for different times, and says results "relate only to the test conditions specified". Two ILD figures only compare if they were tested the same way.
Firmness names are each maker's own
"Plush", "medium" and "firm" are not a shared standard. Our comfort guide groups mattresses as Extra Firm, Firm, Medium Firm and Soft, giving one set of feel levels across brands. You can browse firm, medium or soft mattresses that way.
Coil counts follow the size
A bigger mattress holds more coils, and different coil types run to different counts.
Foam Density: How Much Foam, Not How Firm
Foam density is the weight of a set volume of foam, often given in pounds per cubic foot. It tells you how much material is packed in, not how firm the foam feels. A foam study describes density and firmness as properties that function independently, so a dense foam can feel soft and a lighter one can feel firm.
Two things to keep in mind when you do see a figure:
- Compare within one kind of foam. Latex foam is inherently denser than conventional polyurethane foam, so a latex figure and a polyurethane figure aren't a fair contest. If you are shopping memory foam mattresses, compare memory foam with memory foam.
- Treat density as a clue. In lab testing, higher-density foams typically lose less thickness after long compression (a lower "compression set"), which suggests better recovery. That is a clue to how a foam holds its shape, not a lifespan or a comfort score. The same study notes that denser foam's extra resistance to load "does not always translate directly into improved comfort".
What ILD Measures, and Why One Number Isn't the Feel
ILD (indentation load deflection), also called IFD, is the force needed to press a flat indenter a set distance into a foam sample: a higher number means a firmer sample, not a better or thicker one. ASTM D3574, the standard set of test methods for flexible polyurethane foams, says its data apply "under conditions of the particular test" and are not necessarily the same in other environments in use.
Here is what one sample's number leaves out:
The whole stack
Feel comes from comfort layers, transition layers, and a foam core or coils. The foam study found standard tests only partially capture comfort-relevant behavior in layered builds, and swapping layer order changed how some lab stacks responded.
The cover and quilting
The same study notes cover materials "are known to affect" the foam underneath.
Warmth and speed
Memory foam stiffens when it is cooler and when it is pressed quickly. It can feel firmer at first touch, then soften as you lie still and warm it.
Your body
A heavier body sinks further and reaches the firmer layers below; a lighter body stays nearer the surface.
Coil Types, Gauge and Count
Coil units fall into four families, described in a US International Trade Commission report.
| Coil type | How it's built | What you tend to notice |
|---|---|---|
| Bonnell | Hourglass coils with a round, knotted head, laced together with spiral wire | A connected unit that moves together; generally the lowest-priced innerspring units |
| Offset | Hourglass like Bonnell, with flat tops and bottoms and a squared head, also laced together | A connected unit; the report says offset systems usually produce less noise |
| Continuous | Whole rows formed from a single S-shaped piece of wire | A connected unit; commonly a high coil count, with less steel and much thinner wire |
| Pocketed (wrapped or encased) | Each coil in its own fabric pocket, pockets glued together rather than wired | Coils move more independently, which is why they are used to reduce movement across a bed |
Connected coils, the kind in many innerspring mattresses, tend to move as a unit, which often feels bouncier and lets movement travel. Hybrid mattresses put foam or other comfort layers over a coil unit, often pocketed, and some add a layer of small microcoils in the comfort layers.
Gauge is the wire's diameter, and a lower gauge number means thicker wire: the report lists 12.5-gauge wire at 2.05 mm and 15.5-gauge at 1.45 mm. Thicker wire makes a stiffer spring, all else equal, but coil shape, height and what sits on top shape the feel too. Counts only compare for the same size and coil type, since microcoils raise the total.
Do Higher Numbers Mean Better or Longer-Lasting?
Not on their own:
- A higher ILD means a firmer sample, not a better one.
- A lower gauge means thicker wire, which makes a stiffer spring.
- A bigger coil count depends on the size and the coil type.
- Denser foam is one clue to shape retention, not a promise.
Wear has its own lab test. A fatigue test pounds foam repeatedly and measures lost thickness and firmness, and its standard says those losses "are related to, but are not necessarily the same as, the losses likely to occur in service." In real life, wear depends on the kind of foam and each layer's thickness, the coil build, the support underneath, and following the maker's care instructions.
So judge durability piece by piece. Ask about each layer, and check which foundations and bases the maker calls for.
Price follows the same logic. Cost can come from more material (denser foam, more or thicker layers), the coil system, or extra components such as a microcoil layer, and the tag alone doesn't say which you are paying for. If you can't feel or find a difference between two mattresses in the same feel group, the extra cost may buy something you won't notice.
The Lie-Down Test That Compares What Numbers Can't
The comparison a spec sheet can't make is one you can feel. At a Mancini's Sleepworld location, one of 50+ locations across Northern California, you can lie on mattresses from many brands side by side.
- Start from a support level. Settle how much support you need before any number comes into it; SleepMatch can suggest a starting point. Specs are tie-breakers inside that level.
- Shortlist by feel group. Pick Extra Firm, Firm, Medium Firm or Soft from the comfort guide.
- Try one coil type from two brands. Two pocketed-coil mattresses in your feel group show what the layers above the coils change.
- Then try two constructions in one feel group. An all-foam and a hybrid, say, both Medium Firm.
- Lie still in your real sleep position for several minutes. Bring your own pillow, and give memory foam time to respond.
- Roll over, sit on the edge, then go back to the first. Differences often show up on the return trip.
- Test together, then ask. If you share the bed, lie down side by side, then fill in the spec sheet below for your top two.
Your Spec Sheet to Take Along
When figures aren't listed, a Sleep Specialist can tell you what the maker publishes about each layer. Fill in one column per mattress on your shortlist.
| Ask | Why it matters | Mattress 1 | Mattress 2 |
|---|---|---|---|
| Every layer, top to bottom, and how thick? | Feel and wear come from the whole stack | ||
| A density figure, and for which foam layer? | A figure means little without the foam type | ||
| An ILD, for which layer, and how was it tested? | Different methods give different numbers | ||
| Pocketed or connected coils, and any microcoils? | Changes how the bed moves and what the count includes | ||
| Support-coil gauge, and is the count for this size? | Both only compare like for like | ||
| Which base does the maker call for, and what care? | Support and care both affect wear | ||
| Which mattresses from other brands here are built the same way? | Sets up a fair side-by-side test |