Friday, February 27, 2009


We have high density, low density, high compression, low compression,   5 ,10 or 15 year, open cell, closed cell, latex, visco-elastic, memory, craft,outdoor and camping foam.  And all you wanted was some new foam for the chair pads in the kitchen.

So here you are, the Foam dictionary:

Density: refers to the amount of material per square foot. High density has more material, low density has less. This figure is usually expressed in pounds per cubic foot - how much  a piece of foam 12” x 12” x 12” weighs.  Or you may hear high, medium and low density. A number 1 density means the foam weighs 1 pound per cubic foot. 

Compression:  The number of pounds of pressure it takes to compress the foam 1 inch. 40 compression foam takes 40 pounds to compress.  This is referred to as the ILD  ('Indentation Load Deflection'  and it is actually a bit more complex than this simple definition but it’s close.) Typically a high density foam requires more compression to flatten it, but this is not a rule.

Closed cell: The very firm  foam  that  is used, for example,  to construct a packing case that mirrors the shape of the object being packed.

Open cell: the holes are not independent, they run into each other - take a close look at a sponge.

Latex: made from rubber, not petroleum products like most foam. Because of it’s resistance to  mold and mildew this is the most hypo-allergic type of foam.

Memory: a type of visco-elastic (latex)  foam that conforms  closely to the object being placed on it (like you).

Craft:  Inexpensive open cell polyurethane foam

Outdoor: An open cell foam with big holes that are large enough for water to pass through. This is the best stuff for out door patio furniture or boat cushions.

Camping and  craft: inexpensive foam, usually black in color, wears out quickly.

5, 10 or 15 year - the number of years of average use it will take to cause the foam to stay compressed when pressure is applied.

Testing foam by squishing it between your fingers will tell how hard you have to press your fingers to squish the foam. Not much else. If you want to know more about the foam you are buying, ask the seller. If they can’t tell you the density, or compression, or year rating assume that you are buying a low quality foam.

I hope this helps de-mystify foam a bit. Once again, if in doubt go to a reputable dealer, tell him your needs and ask for his advice. Prices vary from supplier to supplier and are usually directly related to quality but you should ask. Also remember that foam can not be returned once purchased so make sure you are buying the right one.

Usually for foam that will be used daily such as  chair pads or sofa cushions, a high density, high compression foam will last the longest. But, you may not want a really hard seat, therefore you will want to find a high density, low compression foam.   Or, you may use a high density, high compression foam as the inner core with a memory foam top layer. Most foam cushions on a sofa or in a cushion will have been wrapped with a quilt-batt  like substance, usually dacron or teralyne, that softens the look of the foam and rounds the edges a bit. 

Price of foam:  Some retailers sell foam by the foot or meter per pre-cut width, most foam suppliers calculate the price based on board feet. This is a piece 12” x 12” x 1 inch thick. If the piece was 2 inches thick, it would be 2 board feet. Currently the price of  hi-density 15 year foam is  about 3.50 per board foot.   This means that a sofa cushion 30 x 26 x 6  will cost about 114.00.  Why so much? The only answer I have been given over the last few years is that there were 2 plants producing the raw product for foam in North America prior to Katrina. One was destroyed in the hurricane and this resulted in the high prices. I don’t know if this is true or not but there was a huge jump in foam prices after the hurricane and these prices have not gone back down. 

How to cut foam: Most foam sellers will cut the foam to the shape you need. Take a paper pattern of the shape. Remember too that in order to have a really snug cushion the foam is often cut about 1/2" larger than the finished size. This is up to you. Be careful with this though, if the foam is less than 3" thick or so, it may buckle. 

Cutting foam at home is easy if you use a bread knife or an electric knife.  I bought a new electric knife just recently- cost $8.88 and works very well.  

The following link has good descriptions of most types of foam, including common uses of each type:

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