production technology has greatly improved over the last decade. But
keep in mind that no foam will last forever. One of the first signs
that you might notice is the shape of cushions. They lose their
original shape. If your furniture is older than approximately ten
years, or if it has “rounded” front edge, or if it simple doesn’t offer
you the support that you used to have, then you probably need new foam.
The effect of “rounded” front edges occurs because you tend to use the
front of your edge to a greater degree then the rest of the cushion.
Another common reason is that the foam was never meant to be used for
seating and as a result its lifetime is short.
Besides the height or “thickness” of the foam there are three major
factors that affect longevity of foam: resilience, density, and
indentation load deflection.
High Resilient (HR) foam is a foam material that is produced
to offer a longer useful life than non-HR foam. This foam is also rated
as fire resistant. Resilience is an indicator of the surface elasticity
of foam. The resiliency test determines surface liveliness and
spring-back ability. A piece of foam with a high resiliency will have
greater spring-back. Resiliency is measured in a lab with a Ball
Rebound test. A steel ball is dropped onto the foam sample from a fixed
height. It is expressed as a percentage of ball rebound against the
original height of the ball drop. A “boardy” (an undesirable stiff
surface feel) foam will have low resilience.
Density is normally recorded in pounds per cubic
foot, and is simply
the sample weight divided by its volume. It is really an indication of
quality and lasting comfort. The more dense the foam, the more
resilient it will be. Thus, density is basically equivalent to
performance durability, so the higher the density, the higher the cost.
Low density foam might provide firm support for a while, but it is not
very comfortable and it will soon lose its shape and support. Only high
density foam will properly conform to your body year after year,
compressing under heavy parts while it supports where you need it. Low
density foam represents foam with a density of 1.9lbs and less. High
density foam represents foam with a density of 2.0lbs and greater.
load deflection (ILD)
ILD is measured by
putting a piece of foam on a flat surface and then
placing a metal weight in the middle of it. The amount of weight
required to compress the foam down by one inch is call the ILD or
compression. The higher the number, the firmer the piece of foam.
18 Very Soft
19 - 45 Medium Firm
46 - 70 Quite Hard
71 - 95 Rock Hard
Above chart is very important. As an instance you want have the same
foam for your loveseat and dining room chairs. Dining room chairs will
require higher ILD. The comfort factor, or "support ratio" is the ratio
of the 25% to 65% ILD readings. A good comfort factor is between 18 and
35. The harder (compression) the foam does not necessarily indicate a
better quality. For example foam can have compression range of 115-125
lbs but density of only 2 lbs/cubic foot. This can be the hardest foam
on the market but because of low density doesn’t make it long lasting.
Density is better measurement of the quality of the foam product. By
engineering compounds carefully it is possible to achieve different
compressions in the same density giving a range of feel and cushioning.