How Is Memory Foam Graded?

Viscoelastic memory foam is temperature sensitive; it softens in warmer temperatures

, and firms up in colder conditions. This explains why it feels firm when you first lie down, but within 4-5 minutes it begins to soften and conform to your body. Memory foam mattresses are actually graded based on viscoelasticity, firmness, durability, resilience, and strength.

Density is a key factor to consider when purchasing a memory foam mattress. It also happens to be one element of the grading system. Some might be under the impression that density tells you how firm a mattress is, but it actually is just a reflection it's overall weight. A heavy mattress is therefore more dense, and contains more materials and chemicals. The result is that it will be more viscoelastic.

The best density is thought of as anything above 4 pounds, though some customers have reported that they prefer as low as 3 pounds. For those who want the best combination of comfort and support, 5 pounds or more is considered best.

Memory foam is also graded by how firm it is using the ILD rating system. The formula for this rating is figuring out much weight is needed to make a 25% indent into the mattress. For example, if the rating was 15, this would tell us that 15 pounds was needed to compress it by 25%. So the higher the rating, the more firm the foam is. Most mattresses have a rating somewhere between 12-16.

Certainly the base will be firm for support, while the top layer softer to reduce pressure points. More than a few manufacturers however either don't test ILD, or won't release it to the public. Though, this information really isn't indicative of quality.

Resilience is another element that is measured. It's tested by dropping a steel ball from a particular height, and then measuring how much the memory foam recovers. Ideally, the top layer should actually have low resilience. The reason is so it doesn't push back against the body, which causes pressure points. For support, the base must have a good amount of resilience. Also, a highly resilient base will make it that much more durable.

The last component of the grading system is tensile strength. This refers to how much force is needed to stretch the mattress to the point where it begins to rupture. Quite frankly, this really doesn't provide any insight into the quality or durability of memory foam.

The trouble with memory foam mattresses is that manufacturers reveal little information about them. Some won't even list the density.

by: Marsha Walderson

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