Differences & Similarities Between Foam Density, Weight & Firmness

3d render of different foam mattress layers

When it comes to foam, the buying process is simple. However, there can be potential confusion when it comes to a foam’s density, weight, and firmness. From a basic perspective, these three terms are understood. However, when applied to the foam industry, the meanings of these terms can be altered to better fit the needs of the industry. As such, there can be some questions and misunderstandings as to what these terms mean along with their relationship and differences. This article is intended to alleviate any questions and misunderstandings that you may have.

Foam Density

Foam density is the mass of a foam’s material within a cubic foot. The denser the foam, the more compact the foam material is. This, in turn, makes the foam heavier. A foam’s density is characterized by pounds and is determined by taking its mass and dividing it by its unit volume.

Polyurethane foam stacked on top of each other

Polyurethane Foam – the lowest density foam we offer here at Foamonline.com at 1.2 lbs.

Let’s use an example. In the foam industry, foam is measured in pounds per cubic foot. As such, we take a cubic foot of Memory foam and measure it out. It weighs 3 lbs. This 3 lbs. foam weight is then divided by its unit volume – in this case, 1 cubic foot. 3 divided by 1 equals 3. As such, the memory foams density is 3 lbs.

Another example. If the memory foam was 10 cubic feet and weighed 30 lbs., it would be divided by the unit volume, which is now 10 cubic feet, and the foam density would still be 3 lbs. This example also aids with confusion over foam density and foam weight. There is often interchangeability between foam density and foam weight that can lead to confusion. Per this example, the memory foams density or material weight is 3 lbs. and its overall weight is 30 lbs. That is why it can be important to distinguish between the density or material weight of foam and its overall weight.

Importance of Foam Density

Foam density is important because it is connected to the quality and durability of foam. For example, a Lux foam mattress with a foam density of 2.2 lbs. would not be as comfortable or long-lasting as a Latex foam mattress with a density of 5.6 lbs. This is because there is more compressed foam material in Latex foam than there is in Lux foam. As such, a Lux foam mattress will deteriorate more quickly, leading to sagging, indentations, and a general lessened state of comfort over time. That is not to say that Latex foam would be better used for all applications. While Latex foam would be better used as a foam mattress, Lux foam would find better usage in couch cushions, automobile seating, or in a multi-layered mattress.

Perhaps this comparison chart can give a better visual understanding of different foam types and their relationship to density:

Foam Type (Density)
Quality
Durability
Cost
Polyurethane Foam (1.2 lbs.) Low Low Very Low
High Density Foam (1.9 lbs.) Medium Medium Low
Lux Foam (2.2 lbs.) Good Good Medium
High Resilience Foam (3.0 lbs.) Very Good Very Good High
Memory Foam (5.0 lbs.) Excellent Excellent Very High
Latex Foam (5.6 lbs.) Excellent Excellent Very High

Foam Weight

Foam weight is the physical weight of the foam. So, if you purchase a 10 cubic foot piece of foam at a density of 5 lbs., the weight of that foam would be 50 lbs. (50 = 10 cubic feet X 5 lbs. density). The foam density remains 5 lbs. Keep in mind that foam mattresses can become quite heavy as you increase the thickness and size, especially when the foam is dense. Plan accordingly if it is.

Foam Firmness

Foam firmness is how much a foam compresses when pressure is applied to it. Firmness is a simplified way of saying Indent Load Deflection (ILD). All foam types have an ILD rating. To get an ILD rating, a 15” x 15” x 4” foam block has pressure applied to it by a circular disk measuring 1’ in diameter and 4” thick. The ILD rating is achieved when the circular disk compresses the foam by 25% of its thickness, in this case 1”. The amount of weight applied to reach this target percentage is the ILD number that the foam receives as its firmness.

For example, if 50 lbs. of pressure is required to compress a block of foam 25%, the foam is given an ILD 50, which is firm. More force is applied to firmer foam types and less force is applied to softer foam types. The higher the ILD number, the more force is applied, and thus the firmer the foam. Most foams have an ILD between 15 and 70. However, foam can go even higher, with Charcoal and Closed Cell foam that we sell here at Foamonline.com having an ILD 90 and Rebond foam having an ILD 150.

Closed Cell Foam

Closed Cell foam – it might look dense but is a 2 lbs. density.

Foam Density vs. Firmness

There is also confusion surrounding foam density and foam firmness. Many people think that a higher foam density means a firmer foam. This is not the case. A low-density foam can be firm and a foam that is high in density foam can be soft.

If you view our ILD Chart, you can see that the foam we offer come in many different foam firmness’s. Foam firmness’s range from very soft to extra firm. For example, we offer High Resilience foam in both a 2.8 and 3.0 lbs. density that is also available in most all firmness’s. As such, foam density has no correlation with foam firmness. Foam firmness has nothing to do with the quality or longevity of foam. It is simply used to determine how much a foam compresses when pressure is applied.

When purchasing a foam mattress, some of the characteristics chosen such as density and thickness is budget-oriented while firmness is mostly a personal preference. However, an important aspect that should influence one’s decision is the weight of the user/s. For mattress density and thickness, the heavier the person, the denser and thicker the mattress should be to support their weight. If the mattress is low density, it will lack support and lead to excessive sagging. If the mattress is too thin, it can bottom out and cause excessive pressure points. This is most notable when sleeping on your side.

The lighter the person, the less dense and thinner the mattress can be to support their weight. Lighter people do not need the same conformity from higher density foam to provide pressure relief that heavier people need. A thicker mattress could be purchased but is not a cost-effective purchase.

The chart below can give you a better understanding of what mattress thickness is appropriate for you:

Mattress Thickness, Firmness
Physical Weight (pounds)
Description
Low Profile Mattress, Medium Soft
2 to 5 inches
100 and under Used for cribs, folding beds, and mattress toppers.
Slim Mattress, Medium
6 to 8 inches
100 to 150 Ideal for people that have difficulty getting in to and out of bed, as well as children.
Standard Mattress, Medium Firm
8 to 10 inches
150 to 200 The typical mattress size found on the market. It usually consists of a couple of different foam layers for comfort.
Standard Mattress, Firm
10 to 12 inches
200 to 275 A 12-inch mattress will typically have shock-absorbing foam as the bottom layer and transitional layers of various other foam types.
Thick Mattress, Etra Firm
12 + inches
275 + Mattresses in this thickness have various layered foams and other materials. However, as height increases, convenience decreases.

With mattress firmness, the heavier the person is, the firmer their mattress should be. A firmer firmness will provide ample support to pressure points for side sleepers and general comfort. Conversely, if a mattress is double digits in thickness and is a soft firmness, a heavy user will sink into their mattress and will have difficulty getting out. A lighter person will want a softer firmness. We recommend medium to medium-soft. Lighter people exert less pressure, so a softer mattress will conform to their body shape better and provide more support to their pressure points.

Help

If you need more information about specific types of foam, visit our Foam Types page. If you have more questions or need more information, feel free to contact us.

37 replies
  1. Thomas
    Thomas says:

    Hi,
    We are looking for foam for an application we have in the neonatal intensive care units and delivery rooms of hospitals.  We are looking for a foam piece with the dimensions of 623mm x 467mm x 40.5mm.  
    ILD of 9lbs at 25% and density of ~3-5 lbs. 
    We are prototyping at low quantities to begin with to make sure the foam works then we will scale up making 22k of these beds. Please let me know if you have anything in this range please.  Thanks! 
    Thank you! 

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Thomas,

      The most commonly used foam for infants is a medium quality 1.9 lb High Density in medium-firm ILD 36. A lower quality 1.2 lb Polyurethane foam will not be sufficient because the foam will take to the shape of the infant’s body and will not provide the proper support. It will soften and indent in the center area while remaining firmer around the edges. You have referenced an excellent quality 3 lb High Resilience type foam in an ILD 40 that can also be used in this type of application. There is a third good foam type called Lux at 2.2 lbs in an ILD 36 that is also within the range of your requirements.

      Reply
  2. Stephen
    Stephen says:

    Hi. I’m looking to make seat cushions for the bucket seats in my car. They would need to be no more than a half inch thick so head room is not compromised. I would need a very high firmness foam so that it wouldn’t bottom out. What would be the firmness I should aim for to make the seats just a bit softer? Currently I make due with just sitting in the bare shell, so any cushioning is going to be an improvement. But I understand there are some foams that are extremely dense and wouldn’t make much of an improvement. I am about 240 pounds. Thank you.

    Reply
    • FoamOnline
      FoamOnline says:

      The issue is that thinner foam is less firm than thicker foam. Half-inch thick foam is very thin and will bottom out easily at 240 lbs. If you are going this route, then our recommendation would be to use half-inch thick Rebond foam at an ILD 150 (Extra Firm). That is the firmest foam we offer.

      Reply
  3. John Platos
    John Platos says:

    Hi I’m looking to make a reflex boxing bag that will need to withstand constant hard punches without deforming. I’d like to use a very firm foam core. Do you have any recommendations? Thank you.

    Reply
    • FoamOnline
      FoamOnline says:

      Hi John. There are two foam types that will work. The first foam type is known as Rebond, and is very heavy at 5 lbs per cubic foot and very hard in an ILD 150. The second foam type is known as High Resilience, and is heavy at 3 lbs per cubic foot and hard in an ILD 70. The Rebond type foam comes in the firmness extra firm only and the High Resilience type foam comes in a variety of firmnesses, ranging from very soft to extra firm. Both of these foam types are of excellent quality.

      You can price quote or order either of these foam types by following this link: https://foamonline.com/cube/

      Reply
  4. Andrew N Dart
    Andrew N Dart says:

    I need to repad 12 wooden prayer kneelers (prie Dieus) in a Eucharistic Adoration Chapel. They get a lot of use. Which foam do you recommend I buy. I have no experience.
    Peace, Andy

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Andrew. The foam type used in wooden prayer kneelers for longevity and durability is High Resilience. Being used as a kneeler with a large amount of weight placed on the foam per square inch, we would recommend that the firmness be extra firm. We would recommend that the foam be wrapped in 3/4 inch thick Dacron to round the edges of the foam as the cover is pulled down tightly.

      Reply
  5. Cynthia Larocque
    Cynthia Larocque says:

    I am completely re-doing a sectional, and I selected thick High Resilience Foam in a Medium Firm as a base since I have a much heavier partner who needs the extra support in the cushion. Unfortunately, my butt goes numb sitting on the Medium Firm since I am small. Since I haven’t made the cushion covers yet and the cushion height can be anything, I’d like to layer the cushions with a top layer of foam (also High Resilience) in either Very Soft or Medium Soft for a soft sit for me, and I was wondering if you could help me with a few questions: Which would you recommend, and in what thickness to go over top the Medium Firm foam for a much softer sit? Also, do I need to layer on both sides of the foam? Thank you in advance!

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Cynthia. First, we would recommend Medium Soft for your cushion. Very Soft will likely sink down too quickly. Second, the foam should ideally be a 2″ Medium Soft top layer. If the cushion is reversible, you could have 1″ Medium Soft on both the top and the bottom of the cushion. Keep in mind that the average height of a sectional from the floor to the top of the cushion after it is reupholstered should be 18″.

      Reply
  6. Sandy C
    Sandy C says:

    Looking for recommendations for foam to make cushions-turned-mattress for our weekend campervan. Constrained to 3″ thickness that will cover the plywood sleeping base when pulled out. We are in the 150 to 170 weight range and at home are used to sleeping on memory foam. Would the high resilience medium firm be a good pick? Also, is a Dacron wrap recommended? Thanks for a great, easy-to-use website!

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Sandy. Thank you for your kind words! Based on your description, we would agree that the foam type and firmness suggested – High Resilience in Medium-Firm, would make a great seat and mattress for your campervan. We would also recommend Dacron in a thickness of 3/4 inches to create a slight crown on the foam.

      Reply
  7. leah
    leah says:

    I am redoing cpr practice pad/chest made out of foam. The recommended (by AHA) push force for cpr is 100-125 pounds and indentation of 1.5-2 inches. so I would like a foam that indents 1.5-2inch when pressured with force of 100-125 pounds. What do you recommend as most suitable?
    Thank you in advance, looking forward to your answer!

    Reply
  8. Daniels BH NG
    Daniels BH NG says:

    Hi,
    I am looking to fill a Queen size bean bag. It is for my paitent who finds bean bag helps him to mould his contours to rest and sleep. This is for a body weight of 80 kg (180 lbs). I need to fill with shredded foam.

    Criteria that I look for:
    (A) a shredded foam that can hold the bean bag position on its own.
    (B) but yet soft enough that it moulds the body contours.
    (C) Not too hot as It is in the tropical climate.

    Of course I shall play around with the volume of the shredded foam.
    Please advise on the type of foam I should buy or even a mix of it (of which do advise the ratio). Appreciate.

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Daniel. We have sold shredded foam for bean bags in the past. Our shredded foam consists of various foam types and firmnesses combined in a 33-gallon leaf bag, weighing approximately 5 pounds and containing approximately 4-5 cubic feet. You can find our shredded foam on our Supplies page, under Filling and Stuffing, or by following this link: https://foamonline.com/product/shredded-foam/

      We would recommend mixing this shredded foam with bean bag pellets in a ratio of 50/50 because shredded foam tends to stick to itself and will not shift to different positions as the beans will. Our bean bag pellets can also be found on our Supplies page, under Filling and Stuffing, or by following this link: https://foamonline.com/product/bean-bag-pellets/

      Reply
  9. Cynthia Larocque
    Cynthia Larocque says:

    Hello! I am looking to re-do my back sofa cushions, and my plan is to do a down envelope over foam. I was thinking of doing about 2″ of baffle box casing for the feathers on either side of a 2″ or 2.5″ piece of foam, using the High Resilience Foam. Do those ratios sound feasible or is there a different recommended ratio of feather width to foam width? What would be the best foam firmness to use for that? Thank you!

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Cynthia. The 2-inch baffle would be slightly thin, which is okay if the cushion foam is between 2-3 inches in thickness. The foam type High Resilience is what we normally use with down envelopes because of its high quality, longevity, and comfort. Feather envelopes tend to be on the softer side, so a Medium firmness would be most common. Some people do not like the softer feel and want a more supportive foam. In this case, the firmness would increase to a Medium Firm for an individual up to 175 pounds, and a Firm thereafter.

      Reply
  10. Kris
    Kris says:

    I am redoing a window seat
    77 in long 14 in high
    3 in on the top and 9 in bottom

    I have 2 dogs that love to lay on it to look out the window and bark at everything that they see
    They weigh approx 25 pounds each.
    I have a cheep one I purchased through Amazon, it held up for about a year.
    Don’t know what kind of foam is in it but obviously not good.
    What do you recommend
    Thank

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Kris. Based on your description, we would recommend the foam type High Density, which is a medium-quality, industrial-grade foam that is used in most average furniture and bedding. We would recommend that the top 3-inch piece be in a Medium firmness so that the dogs will be comfortable, and that the bottom base be in a Medium Firm firmness for support in case others would like to use it as well.

      Reply
  11. Julie LaBorde
    Julie LaBorde says:

    I’m looking to recover patio cushions. What’s the best foam for this and do I need to use a dacron for wrap. The sizes are 18x23x3, the longest cushion being 18x40x3. What is your recomendation?

    Thank you!!

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Julie. The most ideal foam type for outdoor patio cushions would be Dry Fast. After Dry Fast, we would recommend, in order of quality, the foam types High Resilience, Lux, or High Density.

      At 3 inches in thickness, we would recommend a firmness of Medium Firm or Firm, depending on the average weight of the user.

      Outdoor patio cushions are sometimes wrapped in Dacron, it just depends on the desired look of the cushions. If you would like your cushions to have a puffy look, then Dacron would be used.

      Reply
  12. Niamh
    Niamh says:

    Hi, would really appreciate some of your great advice please. I am making a 8ft high fluted headboard using 4″ wide fluted pieces what foam should I use?

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Niamh. Based on your description, we would recommend the foam type High Density, which is of medium, industrial grade quality, in a firmness of Medium Firm. If you’d like the foam to last more towards the 15 year mark, you may want to upgrade the foam type to High Resilience, which is of excellent quality, in a firmness of Medium Firm.

      Reply
  13. Casey
    Casey says:

    I’d like to put a wedge foam under my golf simulator to protect the wall from golf ball impact. Which firmness, inches of thickness and foam would work?

    Reply
  14. Erica S
    Erica S says:

    I’m looking to have some rectangles cut from foam with similar firmness to McMaster P/N 8647K28. Their rating system says “25% compression at 4psi.” Am I correct that this would be an ILD of ~450? Do you have any foams which would match that firmness?

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Erica. We believe that an ILD of 450 will not compress 25% with a load of 4psi. It sounds more like an ILD of around 150, which we do offer under the foam type Rebond. We would recommend purchasing a sample for testing purposes by emailing us at info@foamonline.com.

      Reply
    • FoamOnline
      FoamOnline says:

      Hi Debbie. Based on your description, we would recommend the foam type High Resilience in a firmness of Extra Firm for the seat cushions, and the foam type High Resilience in a firmness of Medium Firm for the backrest.

      Reply
  15. Doris Moeller
    Doris Moeller says:

    The dinette cushions in my RV are way to soft, making us sit too low to eat at the table. What foam would you recommend, we would like the cushions to be very firm.

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Doris. Based on your description, we would recommend the foam type High Resilience in a firmness of Firm. If the average weight of the user is over 250 pounds, we would recommend a firmness of Extra Firm.

      Reply
  16. Teresa
    Teresa says:

    Hi, I need to replace the foam in the cushions of a love seat at a nursing home for nuns. The nuns say they sink when they sit on the cushions and then have a hard time getting up. The current cushions are about 6” thick with a Dacron wrap. What foam density do you recommend that would be firmer and hold up longer?

    Reply
    • FoamOnline
      FoamOnline says:

      Hi Teresa. Based on your description, we would recommend the foam type High Resilience in a firmness of Medium Firm, which is ideal for an individual in the weight range of 140-195 lbs. Any weight past 195 lbs, we would suggest High Resilience in a Firm and any weight below 140 lbs, we would suggest a Medium.

      Reply

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