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For any type of polyurethane foam to be considered visco-elastic, it has to have a few characteristics. It must be sensitive to temperature and pressure and it must be able to return to its original form once pressure and temperature has been removed. Once it is determined that a polyurethane foam as visco-elastic it is considered memory foam and it's graded based on its nature and durability using four different grading methods.
The ILD Rating
ILD stands for Indentation Load Deflection and is a direct measurement of how hard or how soft the memory foam is. A 20% ILD rating is the number of pounds that are required for a 3 inch thick foam mattress with an indentation of 40 square inches to achieve a 20% compression. For instance, if a memory foam mattress has an ILD 20 pound rating it would indicate that the mattress would need 10 pounds of pressure to indent the mattress 10%. The bottom line is that the higher the Indentation Load Deflection, the more firm the memory foam mattress is.
Resilience
This is an interesting measurement. Resilience measures the foams springiness. It's actually measured by dropping a small, steel ball from 36 inches above the mattress and then figuring out the percent of rebound the steel ball has when it bounces off the foam. If the memory foam mattress give a high percent rebound and that mattress will be determined to have a high resilience (so it will be classified as HR foam). The basic rule of foam is the higher the resiliency of the mattress the stronger and more durable the foam will be when exposed to pressure.
The weight of the foam is measured by its density in pounds per square foot. The actual weight of the foam can be determined by the number and amount of chemicals that are used in the polyurethane foam's composition. The higher number of chemicals that are used, the higher the density and visco-elasticity of the foam will be. Density is not determined by the thickness or the hardness of the foam. The thickness and the hardness of the foam is measured with the ILD rating. Most mattresses on the market that are memory foam use a density of 5 or 4 pounds but you can find some that have densities of 2 and 3 pounds.
Tensile Strength
Tensile strength is used to indicate the exact extent to which memory foam can be pulled and stretched until it tears or ruptures. The measurement is determined in pounds per square inch and a percentage of elongation before it tears. This is the least relevant measurement of all for measurements because memory foam mattresses are not often stretched or elongated.
An important fact to remember is that the ratings used for memory foam mattresses can vary greatly between different batches of foam. Also, because of this variation, manufacturers are often unable to determine an exact rating on their final products. For example, a memory foam mattress with a 20 ILD rating could vary from an 18 to a 22 ILD rating for each batch of foam that is created.
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One type of product that has become very popular in the last few years to help you sleep better is Memory Foam.
Memory Foam is a foam made from polyurethane with additional chemicals that add to its viscosity level, thereby increasing the density of the foam.
Fagerdala World Foams of Gustavsberg, Sweden, spent almost ten years perfecting the material for mass production. It was first introduced in Sweden and became known around the world as the Swedish Sleep System. Tempur-Pedic licensed the material and became the US manufacturer.
Fagerdala manufactures foams for insulation, sealing, shock absorption, protection, cushioning, comfort, floatation, filtration, and rigidity.
Fagerdala World Foams is the parent company of an international group specializing in the development, manufacture and marketing of polymer foams.
The group employs approximately 1.500 people and operates 30 factories in 14 countries, with a total building area of 265.000 m². The head office is located at Gustavsberg Harbour on the island of Värmdö, 20 km east of Stockholm, Sweden, to where it was moved in 1999 from the original nearby location at Fagerdala.
It was initially developed for NASA because of its ability to distribute pressure across the entire surface, because it could ease the pressure of extreme G-forces.
Because it eases pressure on the body it is now widely used in medical applications for patients suffering from pressure sores or bed-bound patients.
Previously too expensive for general use it has now become cheaper to produce.
You can now buy memory foam mattresses and mattress toppers.
As a matter of fact memory foam mattresses have become the fastest growing segment in the mattress industry.
There is a true proliferation of companies producing memory foam products and it is difficult to distinguish quality.
The first generation of material just wasn't very durable, and would often compress or crack over time until a Swedish company called Tempurpedic developed a Class product called the Tempurpedic Mattress.
Tempurpedic is still very expensive but worth it.
Not all memory foams are equal. They differ a great deal in quality - density, hardness or softness, response to temperature, and also in their durability.
In looking for the right memory foam there are really a lot of different types and qualities out there.
And while this has also meant that a good number of quality memory foams have come onto the market, it has also meant that a greater number of low quality, cut rate foams have also appeared.
Try to avoid the really inexpensive pads or pillows you will find on the market.
Density seems to be the key factor for Memory Foam.
4 lbs seems to be the perfect density for comfort and quality and a mattress of that kind should last 5 years or so.
Stick with a memory foam that has a proven history of real world durability.
Really look closely at not only the density of the memory foam you are buying, but the source as well. You can trust Tempurpedic because they have a vested interest in assuring that their customers get only the highest quality products.
Tempurpedic, however, is four times as expensive as its competitors.
But there are alternatives.
You do not have to buy a Memory Foam Mattress, you can just buy a Topper made from Memory Foam.
Can I Get By with Just a Topper, or Do I Need a Whole New Mattress? It depends on the shape and the age of your existing mattress.
If your mattress is lumpy, feels uncomfortable and has hollows, forget it.
Here is a tip:
Buy the best bed you can find, then add your own memory foam topper.
About best beds, buy a latex or good foam bed, they just don't wear out.
After 5 years or so, when the top starts to sag a bit, just replace the top.
If you ever buy your mattress or foam over the Internet make sure you can return them because you should try the merchandise at any cost.