Foam & the making of The Barcelona Chair.

Foam, a Definition:

A substance - liquid or solid, that is formed in such a way as to trap many gas bubbles within it.
The Foam used in furniture upholstery is generally a PolyUrethane (foam rubber), but latex rubber is also used sometimes.

Characteristics of Foam Rubber:

Polyurethane foam has two pasic charcteristics that describe its suitability for various uses:

Density: Desnsity is the weight of a regular unity of the substance. For example, one type of foam rubber might weight 5 lbs per cubic foot.

Commercial foam manufacturers generally measure foam density in kg per cubic meter. Ranging from approximately 15 - 50 kg per cubic meter. Where 50kg is the denser foam and therefor is gernally less susceptible to compression.

Resistance and Load Deflection: Measures the change in the cubic dimensions of the foam when compressed by a particular weight of specific size and shape. Or looked at another way: A piece of foam that does not change shape and size significantly under the weight of an 8 inch round metal plate is said to have high ILD, (indentation load deflection). A soft piece of foam would have a low ILD.

Specifically - to compress a piece of foam by 25% (for example making a 4 inch piece of foam 3 inch) by putting a 40lb weight on it, implies that the foam sample in question is very firm - and has an ILD of 40.

Although a somewhat subjective matter - ILDs of between 10 - 24 are considered soft, 25 - 32 are 14pt and 33 - 40 are firm. 41+ are considered to be extra firm.

Foam does soften slightly over time with use. (better quality foam will soften comparably less over time).

Comfort:

Different people consider different firmnesses of foam to be more or less comfortable.

The tastes of countries and cultures vary too. The Americans prefer considerably softer foam than the Germans for example. The average comfort range for a sofa in the United States is 25 - 35, where as the average comfort range in Germany is approximately 30 - 40 ILD.

Another consideration is that comfort is dependant upon the specific usage. An ILD that is comfortable in a sofa, might be too soft for a lounge chair or a mattress.

Non Ignition Foams:

Safety concerns about the flamability of foam rubber, has prompted the creation of many governmental standards for fire resistance in furniture manufacture internationally.

The most demanding being that of the British BS-5852 certification and Californian CA-117.

To make a PolyUrethane foam fire resistant a variety of fire retardent chemicals are added to the compound.

It is worth noting that latex rubber is naturally fire retardent and does not require the addition of chemical additives to meet and exceed the legal requirements for British BS-5852 and Californian CA-117 certification.

Chemistry:

This type of foam is made by mixing polyols, diisocyanates, catalysts, blowing agents, anti microbials, silicone and a variety of other additives that permit the foam to rise freely.

Molds and cutting:

Various chill mold techniques might be used or open topped molds, or continuous production - where the compound is poured onto an inclined belt, which transports it to the cutting facility as it sets. Blocks of foam, are die cut to size using computerized automatic machines, specifically designed for the purpose.

Wrapping:

Foam cushions are wrapped in Dacron or a soft polyester before being upholstered.

The Barcelona Chair:

The foam used in the cushions of the Barcelona / Pavilion Chair is firmer than you would find in your average US sofa. The density generally ranging from between 30 and 36 kgs per cubic meter. It is generally manufacturered using a certified non ignition foam, although if this is a concern for you it is best to ask.