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Density, and its Unique Role in Memory Foam Mattresses, Toppers, and Other Products

When it comes to evaluating and comparing foam, one of the two most important figures is density – firmness being the other. For conventional foam, knowing and understanding the density characteristic can help you select a product that’s best for your needs, whether it’s packaging, bedding, or seating.

With memory foam, the meaning and importance of density is a bit different. In an attempt to clarify how to best use these metrics to your advantage when comparing products, we at Foam Factory, Inc. put together this post to help shine a little light on the subject!

The Lounge Style Pillow is available in 5LB memory foam and conventional Medical Foam

Firstly, it’s important to understand that despite the physical differences between memory foam and conventional foam (specifically, memory foam’s visco-elastic additives and temperature-sensitivity), the way density is measured is the same for all styles of foam. The assessment simply requires the weighing of a 12″ x 12″ x 12″ sample of the material. The weight of that sample is then reflected as the foam’s density value. For example, a 12″ x 12″ x 12″ block of foam that weighs 3LB is a 3LB density foam.

In both regular foam, as well as memory foam, density is an indicator of quality and resilience. If you have two materials with identical dimensions but two different weights, there is more physical performance material in the same amount of space in one product. This means there is more material to support you over time, and more material to break down over time as well, extending its life. The greater the density, the greater the quality of a material. Fortunately, this aspect of density is true across all forms of foam.

How memory foam differs with its density indication has to do with the fact it is a reactionary material. Conventional foam will yield to weight and pressure directly as it is applied. But with memory foam, the visco-elastic compounds in the material react to warmth by softening and yielding more to higher pressure areas for a unique contouring effect. While different manufacturers may have different formulations, when you’re dealing with an extra pound of material overall in 4LB versus a 3LB, or 5LB versus a 4LB, there is going to be more visco-elastic material in the greater density, regardless of the blend-balance of visco-elastic compounds to polyurethane compounds.

What this means for someone looking to buy a memory foam mattress, topper, pillow, or any other product, is that they can expect better and longer contouring in higher density memory foam, compared to lower density foam. Essentially, the higher density has a “better memory!” This should be seen more as a feature, rather than an advantage over lower density memory foam though, as personal preference always dictates the degree to which an individual enjoys the contouring of the material.

This performance variance can manifest itself in a few ways to an end user. Higher density memory foam mattresses and the like can take longer to initially form to your body. If you had two memory foam pillows, one 3LB density and one 5LB, like the two contour pillows in the picture to the lower right, you could see the differences between the two rather easily.

5LB (pink) and 3LB (white) memory foam contour pillows exhibit slightly different performance traits

Pressing evenly on both pillows with your hands, you would notice a few things. Firstly, the 3LB will immediately feel softer than the 5LB, though the higher density will slowly soften and “catch up” in feel, as the warmth of your hand is taken in by the material. This difference in immediate firmness can be more pronounced when the ambient temperature in a space is lower. Memory foam that starts off cooler because of a cooler room needs more time to take in body heat, resulting in a slower softening and contouring when you initially get in bed. Once it is warmed, though, the foam behaves as it would in any other environment.

Secondly, immediately after releasing pressure from the pillows, the 5LB will have a more detailed handprint than the 3LB – things like added depth where a little extra fingertip pressure was provided, and possibly even the wrinkles of your palm and knuckles. The 3LB will still reflect your handprint, but it will exhibit less detail; this speaks to the greater volume of visco-elastic polymers in the higher density material.

Lastly, the 3LB memory foam pillow will return to shape more quickly. Over time, the ability to return to shape is a measure of resiliency, but in new products, the speed with which memory foam returns to form reflects the material’s temperature sensitivity. Lower density memory foam has a quicker reaction time to forming and then returning to shape, behaving more like conventional foam. Higher densities hold formed contours longer. In a memory topper or mattress, this may make movement harder for some individuals, as the position you were in will stay in the foam for a few seconds, as the foam returns and forms to your new position. That longer memory means better contouring, pressure relief, and more of a “sleeping on a cloud” type of feel. For some, it can be too much contouring and softness though, and the lower densities provide something more similar to conventional foam, while still having the benefit of the memory foam feel.

With this combination of factors, memory foam products give customers a little more to consider when making a decision, compared to standard foam. Higher density memory foam products produce a more unique, customized feel, while lower density products have more in common with conventional foam, yet still maintain a degree of temperature-sensitivity. Keeping this knowledge in mind, with the fact greater density still does indicate greater quality and longevity, can help you make a better-informed decision that will hopefully result in your best night’s sleep!

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