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 others poly 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 polyfoam is a good choice, for the budget conscious consumer, who is looking for a no frill, reliable mattress.