What Is Ild Mattress

Helen Skeates
Helen Skeates
13 min read

When trying to explain what an ILD mattress is, it helps to think about how firm or soft a mattress is. It’s a standard for measuring mattresses, particularly ones made of foam materials like memory foam and latex. We’ll break down ILD ratings so you can learn more about them without having to memorize a bunch of acronyms.

We also suggest that you read this helpful guide on choosing the right level of firmness for your mattress. In addition to knowing where you fall on the ILD scale, you should also be familiar with how firm your mattress is. It is important to keep in mind that ILD is not the only factor that determines the firmness of a mattress.

Everything To Know About ILD In Mattresses

What is ILD?

To determine how firm or soft a mattress is, you can look at its Indentation Load Deflection (ILD). Other foam products, like furniture and seats, also feature the ILD value. The ILD indicates how much pressure is required to compress the foam.

What is ILD? | SleepOnLatex.com


Impression force deflection, or IFD, is the same as ILD. Since both ratings are based on the amount of force required to compress a foam, they can be used interchangeably. However, it is more common to find ILD ratings on mattresses.

Low ILD vs high ILD

A mattress with a low ILD rating is soft, while one with a high ILD rating is firm. Foam with a lower ILD rating is softer than foam with a higher rating. Quantitative ILD measurements like soft, medium, medium-firm, and firm will also be used by mattress manufacturers.

ILD and firmness

You can tell how soft or firm a mattress is by looking at its ILD value. Since ILD is only relevant to a single foam layer, it is not the only influential factor for firmness. The bed’s firmness is also determined by the other materials used to construct it.

How to Test ILD

An indentation penetrometer, which works like a press, is used for ILD testing.To guarantee that all memory foam ILD ratings are comparable, the testing process is governed by a number of standards. All of the foam samples being evaluated are four inches thick and fifteen inches square. The penetrometer should have a circular indenter with a 50-square-inch surface area for compressing the sample.The foam sample is then laid flat on the perforated base of the ILD testing machine. While the indenter presses down on the foam sample, the perforations allow air to escape.The tester then compresses the foam sample to 75% of its original thickness in order to bring its temperature up to testing standards. Now we’re at phase two, where compression occurs at a rate of 4 mm/s.

Six minutes after the end of the warm-up is when the real test begins. The foam layer is compressed to between 25% and 75% of its original thickness at a rate of 0.83 mm/s by the testing machine. After one minute of compression, the tester records the firmness rating in ILD (25% ILD).After all other tests have been completed, the sample will be compressed to 65% of its original thickness and the value recorded one minute later.Each test will yield a different result, but ILD values can be anywhere from 14 (very soft) to 44 (very firm). Indentation load deflection (ILD) ratings for polyurethane foam[1] can range from 20 pounds at 75% compression to 50 pounds at 65% compression. Most manufacturers of foam products only report the results of the initial 25% of the latex ILD test.

Which Variables are Considered During Testing?

In order to ensure consistency across multiple product specifications, ILD testing is conducted to determine mattress ratings. Compression loads, material dimensions, and ambient conditions are all factors that are accounted for in these norms. However, testing standards are rarely met in real-world production and use settings, and neither are conditions nor mattress materials.What follows is a discussion of the factors that influence the indentation load deflection and the firmness of a mattress.

Material Thickness

The thickness of the foam is another factor influencing ILD. The ILD of foam increases in direct proportion to its thickness. There can be a three-pound difference between the ILD ratings of a four-inch and a five-inch foam layer, or a four-pound difference between the ILD ratings of a five- and a six-inch foam layer.


A mattress’ ILD can drop as the temperature rises. In order to provide an ILD range that accurately reflects firmness throughout the year, most manufacturers subject their materials to seasonal temperature changes during testing.Your body heat while you’re in bed is another factor to consider in relation to the temperature. Even the firmest mattresses will soften slightly when they absorb enough heat from your body. This response is preferred by most people because it allows the foam to conform to their unique body shape, reducing pressure points and encouraging correct spinal positioning.Some mattress companies create their products to maintain their ILD within a narrow temperature window.Dunlop Latex Mattress Topper | Order Dunlop Mattress Toppers - Latex  Mattress Factory

Foam Type

When conducting tests, the type of foam used is an important factor. Foams in the polyurethane, memory foam, and latex categories don’t feel the same after prolonged use, even though they all have the same ILD rating.Polyfoam, because of its open-cell structure, springs back to its original shape after being compressed. Memory foam, on the other hand, is dense and viscoelastic, so its structure is impermeable to fluids. Memory foam has shape-recovering properties thanks to fillers like blowing agents and gasses, so your handprint will fade over time.


In the United States, all factories use the same ILD rating chart and must adhere to a wide range of manufacturing standards. There is a fair amount of variation in firmness between products with the same indentation load deflection rating, despite the high degree of standardization in this industry.The materials, procedures, and environmental factors used in each manufacturing facility contribute to the wide range of possible outcomes. To differentiate themselves in the marketplace, many brands use proprietary ingredients and design elements in their products. The load-bearing capacity and the firmness of foam products are profoundly impacted by these variations.You can learn about a mattress’s performance in tests by reading the brand’s product descriptions and specifications.

What Are ILD Ratings?

The ILD rating, also known as the 25% ILD rating, is the amount of force in pounds required to compress a 4-inch thick layer of foam to that depth. You can use the ILD scale to distinguish between mattresses that are soft, medium-soft, medium, and medium-firm. Knowing the ILD ratings of mattresses is crucial for picking the right one for sleeping on.

Soft mattress

A mattress is considered soft if it has an ILD rating of 19, 20, or 21. Because of how deeply your body will sink into the foam at these values, it may not be the best sleeping surface. You can’t maintain a healthy sleeping posture, which is why the foam must resist your weight.

Medium-soft mattress

The ILD for a medium-soft mattress is 22 or 23. This level of softness is perfect for kids and anyone who likes to sink in a little without completely giving up their mattress. However, medium-firm mattresses are more common than medium-soft ones.

Medium mattress

Mattresses with a medium level of firmness are the most popular and widely used variety. An ILD of 24–25–26 indicates a medium mattress. Consider a medium mattress if you’re on the fence about purchasing based on ILD.

Medium-firm mattress

A medium-firm mattress is defined as having an ILD of 27, 28, 29, 30, or 31. A medium-firm mattress will not allow you to sink any further than you would on a medium bed with a value lower than 27. If you suffer from back pain, this mattress could be the solution you’ve been looking for.

Firm mattress

The ILD value of a firm mattress will be in the range of 32–36. A score higher than 36 is possible, but indicates an uncomfortably firm mattress. On the other hand, stomach sleepers should opt for a firm foam mattress to maintain spinal alignment.

What Is Firmness Rating 20 ILD?

A mattress with an ILD of 20 is considered to be very soft. A 20 ILD mattress is ideal for those who prefer a firmer surface while sleeping. However, very soft mattresses should be avoided at all costs because they fail to provide adequate support and can cause chronic pain.

What Is The Density Of Foam?

The density of foam is defined as the amount of foam per unit of dimension. If a block of foam is 3 pounds on the scale and its dimensions are 3 by 3 by 3, then its density is 3 pounds per cubic foot. Foam densities as high as 15LB can be found, but 1LB, 2LB, and 3LB are more typical.

The firmness of foam cannot be extrapolated from its density alone. Instead, it gives you a sense of how long the material will last. Because of their durability and resilience, high-density foams are frequently used for furniture.

Frequently Asked Questions

What is the difference between latex and foam ILD?

Many people are curious about the difference between foam and latex ILD ratings. A 4-inch thick layer of polyfoam is used during testing, while a 6-inch piece is utilized for latex items. Polyfoam’s compression modulus is also less than that of latex.We all know that the ILD of thicker materials is automatically higher. Let’s say you’re deciding between two identical mattresses, one with a latex layer and the other with a polyfoam layer. If so, then the extra compression has likely resulted in a firmer latex mattress.The overall quality, density, and ILD value of the other foam layers in the mattress core are also important considerations.

What is the best ILD mattress topper rating?

Pillows with an ILD rating between 24 and 30 are a good compromise for people of varying sizes and sleeping styles. These items, however, are much less thick than a standard mattress. This means that a medium-firm topper will feel softer than a medium-firm mattress.
Indentation Load Deflection - Mattress Testing RatingsIf you want to soften a firm mattress, though, a thin topper with an ILD of 23 or less is an option. However, if you put a hard mattress topper on top of a medium-soft or soft mattress, you will get better support and motion isolation without having to buy a new bed.Think about getting a topper with an ILD of 30 or higher if you’re big and heavy or suffer from back pain.


And with that, I’m done! To review, an ILD mattress is a tool that indicates the level of softness or firmness of a foam product. More significant ILD values indicate greater firmness, while smaller values indicate greater softness.

Keep in mind that just looking at the ILD ratings isn’t enough when picking out a new mattress. You can extrapolate its expected firmness by thinking about its other components. Foam densities are something else you should learn about, by the way.

Helen Skeates

Helen Skeates

Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.