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Foam 101
 JSI > Cushions > Foam 101
 
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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