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JSI >
Cushions > Foam 101
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There are several types
of flexible foams used
for boat cushions. The
most common are
polyurethane and latex
for interiors or PVC and
EVA for cockpit
cushions.
Foam
is graded in density and
compression. Density is
the weight per cubic
foot. Generally, the
higher the density,
the better the quality.
There are filled foams
that will have a higher
density, but is not a
higher quality than an
unfilled foam. Density
will range from 1 pound
per cubic foot (ppcf) to
3.5 pounds per cubic
foot. The useful range
for most polyurethane
upholstery products is
1.2 or 1.3 to 2.3 ppcf.
Compression is the
amount of weight, over a
given area, that it
takes to depress a piece
of 4" foam, 1 inch.
Compression will range
from 15 to 20 pounds,
(typically used as a
wrap over a firmer piece
of foam) to 95 pounds,
(typically used for
packaging or instrument
cases). Most upholstery
products will use a
35-40 pound compression
for seating and 25 to 30
pound compression for
backrests.
The lower density
foams will lose both
dimension and resiliency
over its lifespan. The
higher density foams do
not lose as much
dimension or resiliency.
A 1.4 pound density will
last for about 100
overnights. A 1.8 pound
density will last for
about 300 to 400
overnights. A 2.3 pound
density will last for
about 1000 to 1500
overnights.
Dri Fast or Eva
Dri are polyurethane
foam with the cell walls
blown out, so water will
just pass through. The
density is usually be
around 1.8 pounds and
there are 30, 50 and 75
pound compressions
available.
EVA and PVC foams
are mostly used for
exterior cushions when
water absorption is a
concern. Almost all of
the flotation foams are
very firm.
The PVC products
tend to be
softer and have
a tendency to
shrink. Most
suppliers will
offer 1.5" or
2", not
necessarily
both.
EVA products are
firmer and less prone to
shrinkage.
Steve Meadows
steve@newjsi.com
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