Foam Classifications

How is Foam Graded?

In the UK foam is graded by weight (density kgm3) hardness (newtons) and by class ranging from L to X as shown in the british standard BS3379:1991 (AMD 7126) which is shown on the table to the right.

• Weight (Density in Kilograms per cubic meter)

The weight of the foam is determined by the amount of chemicals used in the composition of the polyurethane foam. The more chemicals, the higher the density and the more visco-elastic it will become. This density will not determine the hardness of the material, this is done through the relative mix of composite chemicals in the foam. Most memory foam mattresses in the UK use a 55 to 60 kilo density, however the density of some visco-elastic foams can be as low as 40 kilos per m3. ( weight is often referred to as LBs per square foot in the USA i.e. it may be a 4LB foam )

• Hardness (Measured in Newtons)

The Newton rating is going to tell you how hard or soft a material is. A soft foam will have a newton reading of from 30 to 85 newtons, hard foams are from 150 to 240 newtons. Visco-elastic foams are hard to calibrate to this as the hardness of the foam changes due to the foam being temperature sensitive . ( Hardness is often referred to as the foams ILD rating (Indentation Load Deflection) in the USA and are expressed as a percentage figure i.e. a 25% ILD rating is the number of pounds required to achieve a 25% compression of a 4” thick foam using a 50 square inch indentation. An example of this would be: - 20lb ILD foam indicates that this foam took 20 lbs of pressure to indent it 25%.

• Resilience

Refers to the foam’s springiness. The term HR foam refers to a highly resilient foam. Some seating foams are sold with a high resilience foam for that feel , however visco-elastic foam on its own has a very low resilience feel as it compresses to the body shape and has little or no bounce. Most visco-elastic mattresses have a base foam that is high resilience to give the mattress a springy feel. A high resilience foam has an irregular cell structure with small and large cell sizes which gives the foam this unique feel. ( In the USA a test that measures the foam’s springiness is performed by by determining the percent rebound of a steel ball dropped from a height of 36 inches. The term HR foam refers to a highly resilient foam that will give a very high ‘ball rebound’ reading.)

• Tensile Strength

This indicates the extent to which foam can be stretched, measured in pounds per square inch and how much elongation in terms of percent of stretch before rupture. This value has very little relevance for mattresses and seat cushion foams because they are not usually stretched and will become compressed only in use. Foams that need a good tensile strength are foams that are upholstered onto the body of a sofa and need to be stretched and tacked into position.

N.B. It is important to remember that all these ratings can vary from each foam batch that is poured and that no foam company can predict an exact rating on their grades each time they produce the final product. As an example, a foam with a density of 33 kilos and a hardness of 115 newtons may actually vary from 32 to 34 kilos and 90 to 120 newtons but is more than likely to be mid spec.

 
Class
Type of Class
Recommended Application
X
Extremely Severe
 Heavy duty contract seats. Heavy duty public transport seats.
V
Very Severe
 Public transport seats. Cinema and Theatre seats. Contract furniture seats.
S
Severe
 Private and commercial vehicle seats. Domestic furniture seats. Public transport backs and armrests. Cinema and Theatre backs and armrests. Contract furniture backs and armrests. Domestic foam mattress cores
A
Average
  Private vehicle backs and armrests. Domestic furniture backs and armrests. Component layers for domestic mattresses (excluding mattress cores)
L
Light
  Padding, Scatter cushions. Pillows

The majority of foam in the UK is supplied to the high UK flammability standards of the Furniture and Furnishings (Fire) (Safety) Regulations, S.I. 1324 of 1988 (amended 1989) (Amd 1993).

The foam being fire retardant to this standard does not mean that furniture if made from this foam will automatically conform to the UKs fire retardency standards. Furniture and cushions may also have to have a fire retardent cover in a schedule 3 category fire retardant material. or an interliner fabric that meets schedule 3 between the foam and the outer fabric.

Other fire standards often quoted are the fire requirements of the FMVSS302 standard. This standard only specifies the burn resistance requirements for materials used in the occupant compartments of motor vehicles and may not be suitable for applications that need to meet the requirements of the furniture and furnishings standard. please make sure that if a foam states this requirement it also meets the furniture and furnishings standard if it is to be used in a domestic environment.

Being fire retardant does not mean fireproof. All foam will burn, so we advise foam only to be used in no smoking areas if possible.
   
   
     

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