How Foam is Graded and Classified
What is Foam Density? (weight in pounds per square foot lb/ft3)
The density of polyurethane foam and latex is the weight measurement of how much foam or latex is contained in a cubic foot. The more foam per cubic foot, the higher the density and the heavier it becomes. This density will not determine the hardness or firmness of the foam, this is done by using the ILD rating structure below.The density rating gives you an idea of the durability of the foam. The higher the number, the better it's ability to provide support. The density number is only an approximation of the weight and the number can vary a little higher or lower each time new foam or latex is poured.
Weight (Density in pounds per square foot):
1-Get the size & weight of the foam.
ONE CUBIC FOOT = 12" x 12" x 12" = 1728 CUBIC INCHES
2-CUBIC FEET OF FOAM = (LENGTH X WIDTH X HEIGHT) Divided by 1728
3-DENSITY = WEIGHT OF PAD Divided by CUBIC FEET OF FOAM
The ILD rating is going to tell you how soft or hard your foam is. The 25% ILD rating is the number of pounds required to achieve a 25% compression of a 4" thick piece of foam using a 50 square inch indentation. An Example of this: 20lb. ILD foam indicates that this material took 20 lbs. of pressure to indent this foam 25%. Remember that the higher the ILD, the firmer the foam. This rating is the same as the abbreviation IFD (Indentation Force Deflection). IFD is still used, even though ILD was created for the purposes of grading polyurethane foams. A lower ILD foam, for the top layer of your mattress or topper can be an advantage in relieving pressure points. However, too soft of an ILD or too thick of a comfort layer, especially without enough support from the core, can sometimes lead to back issues. The finest mattresses, layer foams of different densities and ILD's in order to get a soft comfort layer on a firmer resilient support core for proper orthopedic support. It is important to note that these ratings can vary from each foam batch that is poured and that no foam manufacturer can predict the exact ILD rating of the foam being produced. As an example, a 10 ILD rated foam could vary from 8 - 12 ILD each time the foam is poured. It's not an exact science, but it can give you better idea of what you are looking for in terms of compression rating. You can use the foam ILD rating together with the foam's density to get a good idea of the overall make up and quality of the foam.What is Foam Resilience?
What is High Resiliency Foam (HR FOAM) ?
HR foam is the highest grade of poly foam available and weighs from 2.5 to 3 lbs per cubic foot. To qualify as HR foam it must have a support factor of 2.4 or higher. The support factor is important and gives the foam resilience which gives it springiness (rubberized foam). This unique quality is derived from it's exclusive chemical formula that contains a rubber compound and gives the foam a different cell structure than other polyurethane foams.
This formulation makes the foam more durable in all ILD's and is suitable for use in any layer of a mattress including comfort layers. It's more expensive to produce than HD foam, and that's why will you rarely see soft HR foam used in the comfort layer of a mattress, except in those made by smaller manufacturers. Because of the lower profit margin most large manufacturers tend to use low density poly foams and convoluted foam instead in the comfort layers and sell it with an attached "story" in order to maximize profits! An example of such a story is the use of convoluted foam in a mattress. They claim it's superior, because it creates an air flow system, which make the mattress cooler.... Just be careful before you buy into this type of marketing, and investigate the drawbacks of convoluted foam.
On the other hand, some of the best HR foams, can compare to the quality of latex because they have a high density & good support factor, and therefore will last for numerous years.
As a rule, the higher the density of the foam, the more supportive it will be. Standard poly foams will have a support factor under 2.4, HR foams will have a support factor above 2.4. The higher the density of the foam, the better it's ability to provide support.
A word of caution about HR foam. It's among the most commonly mislabeled foam. Often, any poly foam that has a density of more that 2.5 lbs and sometimes lower is labeled HR. You will never be told that it does not have the required support factor of 2.4 or higher to be labeled high resilience. The Internet is filled with false claims of HR poly foam, because most people cannot tell the difference. A good way to find out if you are getting HR foam is to ask for it's support factor (or compression modulus).
What is High Density foam (HD FOAM):
It's a foam that weighs at least 1.8 lbs per cubic foot or more, and can go as high as 3 lbs. The 45 ILD foam is well suited as a support layer under a memory foam or latex topper. It can be used as a mattress and is quite comfortable in the lower ILD ratings (30-38 ILD) It lasts longer and will keep its firmness longer than lower density foams. A HD foam mattress provides excellent support while sleeping, as it conform to your body and provides support. This allows the spine to remain in a natural position, thus eliminating stress on the back and neck. As a result of this cushioning effect, the sleeper enjoys a deeper and more restful sleep, therefor is more likely to awake feeling rested and refreshed. This grade of 2lb high density polyurethane foam is a good choice, for the budget conscious consumer, who is looking for a no frill, reliable mattress.