To be what it is today, memory foam went through decades of development beginning in 1937. It went through quite a few different names as well, until it became that foam that is best known for its “memory.”
So what makes memory foam have memory?
The production of memory foam begins with a polyurethane material that is synthesised and later infused with chemicals. This specific concoction of chemicals gives the polyurethane foam base greater density. The foam also becomes highly visco-elastic, or both viscous and elastic. This means that it is stretchier yet resists stretching out when stress or pressure is applied, and has an improved ability to return to its original state once the stress factor is removed. When you lie down on a memory foam pillow, for example, the viscosity of the foam allows it to readily conform to your head’s shape yet not flatten out against the pressure of its weight. Its elasticity furthermore allows it to return to its own shape when you get up. Plus, memory foam will not wear out easily since it continually resists the natural tendency of materials to stretch away from applied pressure.
Memory foam remembers what it was before you laid your heavy head to rest, and always returns to that original shape to give you the same soft yet supportive cushion when it comes time to rest again. This is the unique property of memory foam that makes it the best known material for sleep. It’s very popular in pillows, but is also becoming increasingly popular in mattress toppers to give that extra layer of comfort and support for tired and painful limbs.
The Factors for Quality Memory Foam
Not all memory foam final products are created equally. It all boils down to four factors, what was done to ensure their superiority, and how they work together to produce the final memory foam material.
- Foam Density (pounds per square foot), called its Weight
The foam’s weight differs depending on how much of the abovementioned chemical ingredients are added to the synthetic polyurethane base material. The chemicals are responsible for the viscoelasticity of the foam, and this all-important property of memory foam is therefore directly proportional to the amount of chemicals used in its creation. The more chemicals added, the higher the density of the foam. Note that the density or weight does not affect how hard or soft the material is. Always test different memory foam weights of a product to see which suits you best, and check your best weight before you make a purchase.
- Indentation Load Deflection Rating
ILD Rating is the measure of the memory foam’s hardness or firmness in percentages. The percentage rating equates to the number of pounds required for an X% compression rate of a 50 square inch indentation on foam that is four inches thick. The ILD therefore directly measures greater firmness the higher the ILD percentage rating. ILD is also called IFD, or Indentation Force Deflection. As with density, you must test different ILD rated pillows or mattress toppers to find the one that best suits your needs. In general, however, avoid ILD ratings that are too low or too high to provide both adequate support and comfort. Memory foam that is too soft will not have enough support underneath, which can aggravate back problems. Memory foam that is too hard will be rigid and will tend to cause pain because it does not provide enough flexibility to carry your body’s weight comfortably. Ideally, a layered memory foam design will properly disburse pressure points with layers that gradually become firmer below the top layer to give soft comfort on top and firm support at the base.
Memory foam’s resilience equates to the speed and degree to which it can spring back to its original form. The rating is determined by the percent rebound of a steel ball when dropped on the memory foam from a height of thirty-six inches. The higher the resiliency, the more durable the foam is against compression forces. With viscoelastic memory foam, however, less resilience indicates better force dampening, or better absorption of pressure. To choose a high quality pillow or mattress, therefore, it is again important to select a layered design that has lower resilience on top for comfort and higher resilience going down to the bottom layer for support. This design provides you with adequate pressure point reduction on the surface that comes in contact with your body plus extra support below.
- Tensile Strength
This is how far the memory foam can be stretched without tearing or losing viscoelastic quality. Memory foam mattresses are not usually stretched, but this factor is an important one to consider when choosing a memory foam pillow, especially for sleepers who move around a lot and like to squeeze and mold their pillows. The best memory foam materials will have high tensile strength, meaning that they will endure a lot of stretching without wearing out.