In the early 1970's, NASA's Ames Research Center funded a development project designed to create a
substance that could help relieve astronauts of the incredible g-forces experienced during lift-off.  They
believed that one of the key secrets to reducing g-forces on the body was to use a foam material that could
conform to each person's shape and hold this conformity.  While a foam mold of each astronaut's body shape
could accomplish this, any movement would take a person out of this position and create incorrect pressure
points against the body.  Instead, they created a new foam material that was visco-elastic and therefore able to
conform to a person's shape, but then come back to a normal shape once pressure was removed from the foam. 
This could allow an even distribution of pressure or body weight over the entire surface of the foam, but quickly
adapt to any movements of the body.

With this amazing discovery, Fagerdala World Foams of Sweden, one of Europe 's largest foam producing
companies, began experiments in the 1980s to perfect it for consumer use. 

In 1991, the Tempur-Pedic ®, a Swedish Mattress company introduced this material in a mattress form to the
people of Sweden with very well-received results.  In 1992, Tempur-Pedic ® launched the same products in
North America and experienced a similar response.

With the success of Tempur-Pedic ®, other foam manufacturers in Canada and the United States began to
develop their own visco-elastic memory foam material to offer mattress, upholstering and specialty product
companies the ability to allow consumers to have a variety of options and price levels to choose from.

The differences will be outlined in the following paragraphs and hopefully enable the consumer to make an
informed and savvy decision about which foam mattress product best suits their particular needs.

To give a piece of foam memory, you start with a synthetic polyurethane foam material and add certain types
of chemicals which add an increase in weight or density to the foam.  With the addition of these chemicals,
a non-toxic, visco-elastic foam material is created.  However, there are many features along the way that will
help determine what type of memory foam you end up with.   To understand exactly what differences are found
in each final product, you first have to start with understanding how to grade each foam.  

For a material to be Visco-elastic, it will have to be temperature sensitive and have an ability to rebound fairly
quickly and return to its normal shape.  Memory foam is graded by its visco-elastic nature and its durability by
breaking it down into the following grading system:

1. Weight (Density in pounds per square foot): The weight of a foam is determined by the amount of chemicals
used in the composition of the polyurethane foam.  The more chemicals, the higher the density and the more
visco-elastic it will become.  This density will not determine the hardness of the material, this is done through
utilizing the ILD rating structure.  Many memory foam mattresses use a 4 and 5lb. density, but some use as
low as 2 and 3lb. densities.

2. ILD Rating (Indentation Load Deflection): The ILD rating is going to tell you how hard or soft a material is. 
The 25% ILD rating is the number of pounds required to achieve a 25% compression of a 4" thick foam
using a 50 square inch indentation. An Example of this is as follows: 20lb. ILD foam indicates that this
material took 20 lbs. of pressure to indent this foam 25%.  Keep in mind that the higher the ILD, the
firmer the foam. 

3. Resilience: This measures the foam's springiness by determining the percent rebound of a steel ball
dropped from a height of 36". The term "H.R" foam refers to a highly resilient foam that will give a very high
"ball rebound" reading.  In general, the higher the resiliency, the better the more durable the foam will be with
compression forces. 

4. Tensile: This indicates the extent to which foam can be stretched, measured in pounds per square inch,
and how much elongation in terms of percent of stretch before rupture.  This value has little relevance to
memory foam mattresses because they are not usually stretched, and will become compressed only when
slept on.   * It is important to remember that these ratings can vary from each foam batch that is poured and
that no mattress company can predict an exact rating on their mattress each time they produce the final
product.  As an example, a 10 ILD rated foam could vary from 8 - 12 ILD each time the foam is poured.  

What is the initial smell that comes from memory foam?

While the memory foam does not contain toxic ingredients such as formaldehyde or PBDE
(polybrominateddiphenylether), it can have somewhat of a new foam type of smell that can stay for a couple
of days to a couple of weeks, depending on the foam manufacturer. While this smell does not seem to trigger
allergies, it can be a bother initially for people who have sensitivity to smells.  If you do experience this, here are
some tips to help the smell go away quicker.  Air out the room and wash the sheets after the first couple of nights
sleeping on the mattress.  Sometimes a dish of vinegar on the night stand can help nullify the odors. 

What to look for in a good quality memory foam mattress

Obviously it will be important to allow the foam to do what it is best for:  Allowing for a better contouring of your
body shape and therefore less pressure placed on the areas of your body that press harder against the bed. 
However, don't just go by your weight, because if you are tall, then your weight is dispersed over the bed more.
A good memory foam mattress will not need a box spring underneath it to make the mattress feel good. 
You can order a platform base to increase the height of the bed, but remember that this mattress should feel
good if it was placed on an even, concrete surface.

Spring mattresses V's foam mattresses

While a spring mattress was the standard for many decades,  foam mattresses are becoming more and
more popular due to their unsurpassed comfort and overall body support.  While spring mattresses can feel
nice to sit or lay on, they will not offer anywhere close to the body contouring and therefore spinal support that
memory or latex foam can offer.  It will actually cause a trampoline effect and bend inward when pressure is
applied without conforming to the specific bumps and curves of the body.  While foam can shrink over time,
springs can bend and lose their shape over time.  Therefore,  an old foam bed will likely feel better and offer
better support than an old spring mattress.

Is memoryfoam really the best for achy joints?

When you take into consideration the amount of pressure you place on your shoulder and hips if you are a side
sleeper, neck if you are a stomach sleeper or lower back and sacrum if you are a back sleeper, you will realize
that visco-elastic pressure sensitive foam will offer you the best chance for reducing the overall pressure placed
on your joints by contouring them without pushing back against them.  With latex added to a memory foam mattress
it can offer a bit more spring against the concavities like the small of your back or sides, while not losing the ability to
contour and displace pressure points.