What defines foam quality?

Foam quality can be subdivided into categories, according to the suitability for intended purpose of the foam. They are as follows:

• Feel, Comfort and Support Properties
• Durability Properties

Feel, Comfort and Support

Upholstery foam should feel plush and luxurious to the touch, and more importantly, must provide comfort and support to the user. The foam properties which contribute to this are:

Hardness

Hardness is measured in Newtons (N) = how firm the foam feels.

e.g. HS18-35   ST30-130   EN36-100

Hardness is the measure of the foam's ability to support a load - an indication of the suitability of the foam for various applications and its initial feel - not a measure of quality. If foam is too soft, it will bottom out; if it is too firm, it will be uncomfortable. Foams are tested for hardness (load bearing) and must be within a set range or tolerance. Load supporting properties of foam are measured using indentation force deflection (IFD) , particularly the 40% IFD. To find the hardness a standard size piece of foam is compressed by 40% of its height and the amount of force required to obtain that compression, expressed in newtons, is recorded.

Indentation Factor

This factor, whilst is sometimes referred to as the Comfort or Sag Factor, is the ratio of the indentation forces required to indent foam by 65% and 25% respectively. A high ratio occurs when there is a large difference between the two readings and this would indicate initial softness and deep down support/firmness. It is one of the indicators of foam comfort, and a higher indentation factor usually means softer initial feel coupled with good base support.

Resilience

This is the measure of the foams "bounce" or springiness, contributing to comfort and support. It is widely agreed that foams with higher resilience are best suited for seating. The resilience of foam is found by dropping a steel ball onto a standard test piece and measuring the distance that the ball bounces back. The bounce height is expressed as a percentage of the starting height . Foams with resilience above 50% are classified as High Resilience and those with resilience below 15 % are classified as Low Resilience.

Density

Density is the measurement of how heavy the foam is and is calculated as the mass per unit volume - kg per cubic metre (kg/m3).

e.g. AA15-60   MA24-120   EN36-130

Although density itself does not give any indication of comfort or feel, it does affect support, whereby higher density foams of similar hardness provide better support. Hardness is not determined by density ie high density foams can be produced to be very soft and low density foams can be made to be very firm. Therefore, there is no such thing as "hard" or "firm" density. Density affects foam durability and support. Typically, the higher the polymer density, the better the foam will retain its original properties and provide the support and comfort is was originally designed to produce.

Durability

The durability of a product is the measure of its ability to retain the original properties which define its suitability to purpose. Most products, whether natural or synthetic, suffer deterioration in some properties after a period of use, and the extent of any such deterioration provides a measure of durability.

Flexible polyurethane foams are also measured for their ability to resist tearing or shredding. This is important in applications where foams must be handled frequently, such as in upholstering. The test to determine these properties are tensile strength, tear resistance and elongation. They determine the foam's ability to be stretched or flexed without tearing.

Tear Resistance - how easily the foam tears. Resistance of the foam to tearing can vary from about 100 to 400 N/m depending on the foam grade.

Elongation - how far the foam sample will stretch before breaking - can vary from under 100% to over 300% depending on the foam grade.

Tensile Strength - this is the force required to stretch a standard size foam piece until it breaks - can vary from under 50 to over 100 kilo Pascals (kPa) depending on the foam grade.