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July 22, 2008 - Since the introduction of visco memory foam and air chamber
mattresses into the bedding market, consumers and mattress
producers alike have engaged in an ongoing debate: Which
surface truly provides a superior and healthy night’s sleep?
“In our consumer research studies, we consistently hear that
visco-foam mattresses are uncomfortable because they ‘sleep
hot,’” said Mark Quinn, group executive vice president of
sales and marketing for the bedding division of
Leggett &
Platt, the nation’s largest producer of bedding components.
As summer temperatures and raw material prices continue to
climb, the debate heats up. Which mattress will help
sleepers stay cool this summer?
 Putting the
Debate to Bed: Innersprings Sleep Cooler
Recent
research from
Kansas State University’s Institute for Environmental
Research shows that innerspring mattresses
provide and maintain a cooler and more comfortable sleep
environment than visco-foam or air chamber mattresses. In
fact, innerspring mattresses dissipate heat approximately 28
percent* better than
non-innerspring sleep surfaces.
To identify which sleep surfaces sleep coolest, university
lab technicians measured the evaporative heat loss
properties of visco-foam, air chamber and multiple
innerspring mattresses using a thermal manikin designed to
simulate the body weight and temperature of an average
person.
“The laws of physics tell us that evaporative heat loss is a
long-term cooling phenomenon in which the body is cooled
through evaporation of water,” explained Caleb D. Browning,
Ph. D., senior research engineer/physicist for Leggett &
Platt’s IDEA (Innovation, Design, Engineering, and
Acceleration) Center.
By tracking resistance to evaporative heat loss from the
thermal manikin to each of the three sleep surfaces
(measured in Watts per square Meter or W/m2), university
researchers found that the innerspring mattresses averaged
only 110.79 W/m2 of resistance, while the visco-foam and air
mattresses measured 151.45 W/m2 and 160.48 W/m2 of
resistance to evaporative heat loss, respectively.
“In
our analysis of this testing data, we found that innerspring
mattresses encourage evaporative heat dissipation nearly
one-third better than visco-foam or air chamber sleep
surfaces, therefore offering the coolest sleeping
environment of the three,” said Browning.
 Cool Surface Technology
In addition to their superior rate of evaporative heat
dissipation, innerspring mattresses sleep cooler than visco-foam
or air core mattresses because their surfaces cool at an
accelerated rate. Thermal imaging studies conducted at
Leggett & Platt’s industry testing facilities**
showed that the surfaces of innerspring mattresses have an
initial cooling rate that is approximately 40 percent
greater than the foam or air core mattresses.
As illustrated in the attached graph (data from Leggett’s
testing), innerspring mattresses actively dispel surface
heat as soon as a sleeper rolls off the mattress. In
fact, testing showed the initial cooling rate for the
innerspring mattress was 0.91 degrees per second, while both
visco-foam and air core mattresses showed an initial cooling
rate of only 0.55 degrees per second.
Active Air Exchange: The Construction of Cool
Why do visco-foam and air chamber mattresses come up short
in resistance to heat transfer testing? “There are several
reasons why innerspring mattresses offer superior
evaporative and surface cooling qualities,” says Browning.
“You have to consider the construction and active air
exchange.”
The laws of physics state that air movement across or within
a substance will evaporate moisture. As a substance
increases in density, it becomes less breathable and allows
for proportionally less air exchange. Applied to mattress
physics, the less dense a mattress’s construction, the more
active air flow and evaporative properties it allows.
Innerspring mattresses rely on the advanced engineering of
Active Support Technology™ to provide comfort and support,
unlike visco-foam beds that rely entirely of foams and
fibers that can decrease healthy air flow. And while
air-chamber mattresses depend on the flow of air to achieve
personal sleep customization, the air is trapped in chambers
and is not allowed to flow freely and provide the air
exchange necessary to promote evaporative cooling.
Stay Cool, Stay Asleep
Why is sleeping cool important for healthy sleep? Sleep
experts widely agree that body temperature affects the
circadian rhythm of sleep and that optimal sleep occurs when
body temperature is at its lowest level of the day.
The Netherlands Institute for Neuroscience
in Amsterdam reports that sleep regulation has an
evolutionary sensitivity not only to light-dark cycles, but
also to warm-cold cycles. Sleep coincides with low rather
than high core temperature and causes decrease of core body
temperature. Simply put, whenever your body temperature
begins to fall, you will feel tired, lethargic, and drowsy.
Whenever your body temperature rises, you will feel more
energetic, alert and be able to focus better.
A report titled
Help Me Get Some Sleep from the Oregon
Health and Science University (OHSU) recommends that people
avoid exercise for three to six hours before sleep because
exercise raises body temperature for several hours after
completion. The elevation of body temperature makes sleep
difficult since the deepest sleep occurs when the body’s
temperature is at its lowest level of the day.
The Division of Sleep
Medicine at Harvard Medical School
also reports that body temperature
falls to its lowest point during the all-important REM
(rapid eye movement) sleep phase, and that REM propensity
increases when body temperature is at its lowest point in
the evening. “Anecdotally, we have always known that
innerspring mattresses are the superior sleep surface for
healthy sleep, and frequently overhear consumers’ complaints
that visco-foam and air chamber mattresses sleep too hot,”
said Quinn. “These test results only confirm what we’ve all
known for years: innerspring mattresses provide and maintain
a cooler and more comfortable sleep environment than
non-innerspring surfaces.”
*Indicates plus or minus two
percentage points for margin of error
**To ensure test
objectivity, scientists at Leggett asked a human subject to
rest on each sleep surface for one hour in room with a
maintained temperature of 68 degrees Fahrenheit. After one
hour, the subject rolled out of bed and testers immediately
begin capturing thermal images and temperatures changes on a
15 second interval.
About Leggett & Platt
Leggett & Platt (NYSE: LEG) is a FORTUNE 500 diversified
manufacturer that conceives, designs and produces a broad
variety of engineered components and products that can be
found in virtually every home, office, retail store and
automobile. The company serves a broad suite of customers
that comprise a “Who’s Who” of U.S. manufacturers and
retailers. The 125-year-old firm’s continuing operations are
composed of 22 business units, 24,000 employee-partners and
more than 250 facilities located in 20 countries.
Leggett & Platt is North America’s leading independent
manufacturer of: a) components for residential furniture and
bedding; b) retail store fixtures and point of purchase
displays; c) components for office furniture; d) drawn steel
wire; e) automotive seat support and lumbar systems; f)
carpet underlay; g) adjustable beds; and h) bedding industry
machinery for wire forming, sewing and quilting.
For more information, please visit Leggett’s Web site
at
www.leggett.com.
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