There are so many ways to measure a mattress. If you think about it, length, width, height and perhaps even price come to mind. But there is another important measurement which is often overlooked by novice mattress-buyers: the indentation load deflection, often shortened to ILD.  

This mysterious number can frequently be found included in the product descriptions of mattresses without any explanation of just what it means.  You may have bought a mattress many times before without ever once considering just what that strange number might mean. ​

But never fear! That's why we've crafted this handy guide just for our valued customers! In this article, we'll explain in detail the definition of indentation load deflection as well as touch on what different ILD values can say about a mattress's qualities. We firmly believe that a solid understanding of mattress ILDs will prove a valuable tool in your search for the perfect night's sleep!

​What Is Indentation Load Deflection?

Indentation load deflection is a specific measurement created with the purpose of expressing how firm or soft a given mattress is. It is most frequently used for mattresses, but technically can also be successfully calculated for any product made from foam or foam-like substances. It is occasionally also referred to by the name "indentation force deflection" or IFD, though in recent years ILD has become the standard terminology.

The actual calculations behind a given mattress's indentation load deflection are both extremely specific and extremely technical. The official definition of indentation load deflection in regards to mattresses is as follows:

The amount of force (typically measured in pounds) required to indent 4 inches of foam by 25% ​

But what does this mean, really? Think about it this way. When you press down on a mattress, it indents - that is, it "squishes" or goes down. If you have a mattress that is 4 inches tall, and you press down on it with 15 pounds of force, the mattress "squishes" until it is now only 3 inches tall (i.e. by 25% of its original height). This would mean that that particular mattress has an ILD of 15. However, if you had to press down on that same mattress with 25 pounds of force in order for it to reach 3 inches in height, it would instead have an ILD of 25.

In general, it is not required to understand exactly what an individual ILD value means. What is important is to understand that, generally, mattresses with a lower ILD value will be softer, while those with a higher ILD will be firmer.

​Common ILD Values

It is possible to find and purchase mattresses with a wide range of indentation load deflections depending on your firmness preferences. However, over time, some ILD values have proven to be more popular than others among customers.

Nowadays, it is common to find mattresses of the following ILD values being sold:

Soft mattresses will typically have an ILD of 19, 20 or 21. Sleeping on one of these mattresses will cause your body to "sink" into the foam. The material of the mattress will "embrace" you as it bears your weight.  This, of course, does not mean that it is impossible to find a mattress with an ILD value lower than 21 - nowadays, mattresses are extremely customizable, and it is usually possible to find your ideal value.  However, ILDs which are too low may cause the mattress to not support your weight properly as you sleep.

Medium-soft mattresses have an ILD of 22 or 23. They are slightly less popular than the "true medium" mattresses discussed below. However, you may like a medium-soft mattress if you enjoy feeling "embraced" by your mattress but worry about sinking too deeply or experience pain or discomfort from a too-soft bed. Medium-soft mattresses are also popular with young children, who may enjoy the comfort of a softer mattress but for safety reasons should avoid anything with too much "sink".

A mattress is considered to be truly medium, exactly halfway between soft and firm if its ILD value lies between 24 and 26. These mattresses are believed by many sleepers around the world to be the ideal blend of "embracing" and "supportive". As a result, mattresses in this ILD range are typically the most popular overall. If you are unsure about which ILD is right for you, you may want to consider starting out with a mattress in this range


Next up are the medium-firm mattresses, which cover the ILD range beginning at 27 and ending at 31. These mattresses do not have any "sink" at all - the average person will be lying on top of the mattress rather than sinking into the material. A medium-firm ILD is excellent for providing support, especially if you experience chronic pain in your back, shoulders or hips. However, those who prefer a softer, more "embracing" sleeping experience should perhaps seek out lower ILDs, as they may find these values to be too firm.

Lastly, any mattress with an ILD value over 31 is considered to be firm. (Typically, firm mattresses have an ILD of between 31 and 36, with ILDs over 36 being considered too uncomfortable for a good night's sleep). These mattresses are perfect for anyone who needs that extra bit of support at night. You will be lying completely on top of the mattress and will not sink in at all. Doctors often recommend these ILD values to patients with spinal or other bone conditions, especially those which cause pain while trying to sleep.

Of course, when it comes to choosing a mattress, the most important factor is "is it comfortable for you?" However, there are tons of options out there - even just here at Brand Name, we've got a massive catalog which can easily overwhelm a first-time buyer. (Check it out here to see for yourself!) Understanding these common ILD ranges can help quickly and easily narrow down your search for the perfect mattress.

​Outside Factors Can Affect ILD

When shopping for a mattress, keep in mind that ILD is not one stagnant, permanent, eternally unchanging value. Some mattresses are made of several different layers of material, with each layer having its own separate ILD value and the mattress as whole having a final, totally different ILD of its own. This can be the case even if a mattress's separate layers are made from identical materials with identical ILDs. For example, if you stack 4 inches of latex foam with an ILD of 20 on top of 4 inches of latex foam with an ILD of 20, the resulting, 8-inch thick, latex mattress will have  a unique ILD (not simply 20 or 40) which must be calculated separately.

Some mattresses will disclose the ILD of each layer; however, the overall ILD of the mattress itself is the most important value which determines how soft or firm it is.

Adding a mattress pad or topper will also change the mattress's ILD, and can make it either softer or firmer depending on the thickness and material of the topper chosen.  Typically, sheets, blankets and comforters will not significantly change the overall ILD of your mattress, but something like placing a futon or sleeping bag on top of your mattress might. This is why we recommend focusing on ranges of ILD rather than specific values, as there are so many factors which can affect a mattress's ILD throughout the course of its lifetime.

In particular, some materials such as memory foam will vary in ILD on a day to day - or possibly even hour by hour - basis. This is because memory foam reacts to temperature, becoming softer and more yielding at higher temperatures. (This is what creates the feeling of the memory foam molding to the shape of your body as you sleep). Therefore, when you lay down on a memory foam mattress and it comes in contact with your body heat, its ILD will lower. Not only that, but the parts of the mattress in contact with your body will have a lower ILD than those which are not!

​ILD Vs. Density

One important thing to keep in mind about the indentation load deflection of a mattress is that it is not the same as that mattress's density. ILD is a measure of firmness, NOT density. Density measures how much of the mattress's material exists in a given amount of space, and is measured in more complex "mass per volume" units - such as pounds per cubed foot, or, more frequently, kilograms per cubed meter - while ILD is measured only in pounds or kilograms.

However, there typically exists a positive relationship between a mattress's indentation load deflection value and its density. Simply put, this means that mattresses with a higher density tend to also have a higher ILD, and vice versa. Firm mattresses will be more dense, while soft mattresses are typically less so. Latex is typically a dense material, ranging on average from 65 to 85 kilograms per meter cubed. However, different manufacturing techniques can alter both the density and ILD of latex mattresses.

"Fluffy" materials such as cotton and "foamed" ones such as polyurethane will typically have a lower density (and thus, likely, a lower ILD as well). Similarly to latex, memory foam can typically be manufactured in a wide range of densities due to its flexible and adaptive nature.

Because density is, in simple terms, the measurement of how much material makes up any given mattress, most mattresses will decrease in density over time. This is because the material wears out with heavy use, leaving less of it in its original form. The ILD of a mattress can also decrease along with its density. Over many years, even an extremely firm mattress can gradually become "medium firm" or even soft. However, latex, which is an incredibly durable and long-lasting material, does not experience this degradation as quickly or frequently as other mattress components typically do.

​Elasticity / Resilience

The last important property of mattresses is elasticity, alternately referred to as resilience. This measurement is not as closely connected to ILD as density, but does share an important relationship. A mattress's resilience is a measure of how long it takes to return to its original shape and size after being squished or compressed. Resilience can be measured using either time or percentages, with higher percentages indicating greater resilience. (A mattress with 100% elasticity, currently physically impossible to manufacture, would immediately return to its original form in no time at all.)

Typically, mattresses with a low ILD should also be fairly resilient, as too-low resilience could create body shaped "imprints" or "depressions" in the mattress over time. The exception to this is memory foam, which possesses virtually no resilience at all and is marketed specifically because of its ability to conform to the shape and position of the user's body. Higher ILD mattresses do not take resistance into account as much, as the bodies of sleepers using them are creating far less of an "imprint" than they do when sleeping on their softer counterparts.

Latex is an extremely resilient material, and is capable of reaching elasticities up to 70%. This means that a latex mattress will return to its original size and form in only a few seconds after you have gotten out of bed. On the other hand, synthetic foams such as polyurethane are significantly less resilience - usually reaching values of only 40%. It can take several minutes for the "depressions" in a freshly slept-on polyurethane to vanish in the morning.

​How Do I Choose the Best ILD For Me?

As we stated earlier in this guide, our personal belief at Brand Name is that the best ILD for you is the one that makes you the most comfortable. Your personal preference is the absolute most important factor! However, if you are still unsure, we've provided a unique but effective method of choosing the best ILD range for you when purchasing your next mattress: the position in which you sleep.

Yup, that's right! Your sleeping position can be a fairly huge indicator of whether you would prefer a firm mattress, a soft mattress, or something right in the middle. This is because different ILDs are better at supporting different parts of the body, while potentially not providing enough support for others. Over the course of several years and many, many sleep studies, scientists have determined that:

  • Individuals who sleep on their side are more likely to prefer a soft mattress, something with an ILD of around 19 or 20. This is because the parts of the body touching the mattress are "sharp" areas, such as the shoulders and the hips. These areas might experience discomfort or even bruise when placed against a firm, unyielding mattress. A soft, embracing feeling is the way to go!

  • Stomach sleepers usually gravitate towards firm mattresses, with ILDs in the low 30s or possibly as high as 36. These mattresses support the weight of the stomach and pelvis and do not put unnecessary pressure on sensitive parts of the body. Sleepers may also find it easier to get out of bed in the morning from a stomach-down position if they have not "sunk in" to their mattress during the night.

  • Back sleepers by and large did not have a preference for firmer or softer mattresses. The back-sleeping position is typically considered to be the most stable, as it evenly distributes the body weight and therefore requires the least amount of additional assistance from a mattress. If you are a back sleeper who finds this advice unhelpful, we suggest trying out a "medium" mattress with an ILD of perhaps 25 or 26.

If you're still up in the air, read on for a brief discussion of some of the beneficial properties of firm and soft mattresses!

​Why Firm? Or Why Soft?

Typically, soft mattresses are considered to be extremely comfortable. Sleepers get to feel embraced as the material gently conforms to their body. Sharp bones such as those of the hip or shoulder do not provide any discomfort as they are counteracted by the cloud-like mattress. Over time, fidgety sleepers may even find themselves settling more often into one regular sleeping position, as the mattress will keep them in place rather than allowing them to toss and turn as they might on something a little bit firmer.

On the other hand, firm mattresses are popular primarily because of their supportive nature. All the muscles, bones and joints of your body will be carefully supported by a solid mattress beneath you. You will not "sink in," meaning that your weight will be evenly distributed and balanced throughout the night. In addition, doctors typically recommend firm mattresses to anyone suffering from chronic back, shoulder hip or other joint pain. Firm mattresses are also often a great choice if you are regularly sharing a bed with a family member or significant other - they balance the added weight evenly without sagging too much and are typically quieter if one person has to get out of bed earlier than the other.

Ultimately, the choice is yours. The definition of "perfect mattress" is completely different from every single person currently living on this planet. Your search for the ideal night's sleep should be focused entirely on your own comfort. However, understanding indentation load deflection values and what they mean for your mattress can make your search simpler and more stress-free than ever.

At Brand Name, we have an amazingly thorough catalog chock-full of mattresses featuring all sorts of different ILD values, from soft as a cloud to as firm as our dedication to our customers. Whatever ILD you need, we've got it right here for you!

Older Post Newer Post