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| side view HR-30 urethane foam |
Types of Bed Foam
This is the 2nd post in a series of six articles that describe the steps we followed to build our perfect foam bed (see the links in the side bar at right). In the 1st post I described the decision process that lead us to build our own foam bed rather than buying a conventional innerspring mattress and box-spring set. Our backgrounds and "expertise" are described in an earlier (#1) post as well.
Once we decided on the foam bed our next task was to learn as much as we could about the various types of foams available for beds and how to best use them.
We learned that modern foams used in furniture and bedding are made from either synthetic chemical resins or natural latex (rubber), or some combination of the two. Each type foam has very distinct properties which affects the comfort and longevity of the final product, and different foams vary widely in cost. Foams are categorised by density (lbs/cubic ft), which is usually measured between about 1 and 5 lbs per cubic foot, and firmness, expressed as the ILD or IFL number. ILD and IFL numbers for furniture/mattress foam range from about 10 (very soft) to about 50 (very firm). The higher the density the better the foam will hold up in use. A low density foam might last 5 years before it starts to break down whereas a high density foam might last 15 years or more.
Synthetic polyurethane resins
Polyurethane is a synthetic material made from petroleum oil or sometimes plant-derived oils like soybean oil.
Low density (LD) polyurethane is relatively cheap, light-weight (less than about 2.0 lbs/cu-ft) foam used in inexpensive furniture and as filler in combination with more expensive foams. It is not very resilient nor supportive. Like all polyurethane foams it is made from plant and/or petroleum oil.
High density (HD) polyurethane is a heavier, more expensive and more durable foam used in expensive furniture and mattresses, sometimes labelled "LUX" foam. HD polyurethane is still not very resilient but more supportive than LD foam. It does not have the "push back" against deformation the way that HD/HR foam and latex does (see below).
High density/high resiliency (HD/HR) polyurethane is a bouncy version of HD foam, this property imparts the push back which makes the foam more supportive but less "cushy" feeling.
Viscoelastic Memory Foam is a very high density material but it lacks any resilience (memory foam is classified as a high density/low resilience polyurethane). In fact the hallmark of memory foam is that when deformed it tends to hold the shape of the object even after the weight is removed whereas HR foam and latex snap back to a flat surface. Memory foam also tends to become softer at higher temperatures so a warm body seems to "melt" into the surface slightly.
Natural and synthetic latex
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| 3" latex foam; notice holes |
Latex is made from the sap of the rubber tree (natural latex) or from synthetic rubber, blended latex is made from a mixture of the two. You'll also find the term organic latex. When used properly the term means that the natural latex sap is harvested from trees that are grown under certified conditions where no artificial fertilisers or pesticides are used. I'm very skeptical of this designation because it is unlikely that chemicals applied to the tree would end up in the sap thus rendering the distinction meaningless. I believe this is more of a marketing ploy than anything else.
Blended/natural latex foam is a very high density (around 5 lbs/cu-ft) and very resilient (bouncy) material.
Latex foam is made by curing (vulcanizing) liquid latex in a mold. The molds have pins that evenly distribute the heat needed during the curing process. When the cured latex foam is removed from the mold it has holes where the pins were (see photo). These holes are a characteristic of latex making it easy to identify and distinguish from other foam materials.
Talalay vs Dunlop Process Latex
As you research latex foam you'll see the terms Talalay Latex and Dunlop Latex. Latex foam is currently manufactured by one of two different processes. Both natural and synthetic latex, or a blend of the two, can serve as the starting material. The Dunlop process is the older method and results in a denser, somewhat less springy foam while the Talalay process producer a lighter, "softer" foam. This is the only difference between the two methods, Talalay does not infer a more natural process as some retailers deliberately imply!
If you have questions or comments please contact us through our website LivingWithBugs or leave a comment below.
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