Over the years, as foam has become more and more expensive and retailers have pressured manufacturers to reduce prices to compete with imports. Foams have been developed of lesser quality but higher hardness and substituted for the better quality foams. The wash up of this is that the general public has developed a perception that good foam is hard foam and that soft foam is low quality foam. This perception is 100% wrong. A high quality foam can be very soft and, on the "flip side," a poor quality foam can be hard. To try to "right the wrong" (so to speak) the Foam Industry introduced a coding system that enables the end user to know exactly the type of foam they are getting. This also enables them to be able to compare "apples with apples" when assessing value for money. The foam Industry, knowing that the two crucial factors determining the quality of any particular foam are weight and hardness, introduced a code system that advised exactly those two things. Let's look at those two critical factors:-
Weight (referred to as density)
The weight of foam is measured by kilograms per cubic metre. A block of foam measuring 1 metre x 1 metre x 1 metre is weighed and the weight registered becomes the first part of the code. For example if a cubic metre of a particular type of foam is weighed and it weighs 23 kilograms then the first part of its code is 23.
The second crucial measurement of foam is hardness. Hardness of foam is measured in Newton 's. What a Newton is exactly isn't all that relevant other than that it is a measurement of force. The force it measures is the force required to compress a foam to 40% of its thickness when it is cut to 100mm thick. Obviously a soft foam would take only a little force and a firm foam would require a lot more. Soft foams can require as little as 40 Newton's, whilst some very firm foams can require up to 500 Newton's. When the force to compress the foam is measured it forms the second part of the code that determines the type of foam. If the force taken is 130 then the second part of the code is 130.
By adding the two measurements (weight and force) together the code is complete. A foam that weighs 23 kilograms per cubic metre and requires a force of 130 Newton 's to compress it to 40% of its original height therefore has a code of 23/130. And a foam that weighs 35 kilograms per cubic metre and requires a force of 130 Newton 's to compress it to 40% of its original height therefore has a code of 35/130. Note here that the 23/130 & 35/130 have the same hardness (130) but 23/130 weighs less. This would mean they felt the same but the 23/130 wouldn't last as long as 35/130 because it has less weight.
It becomes very simple then to see exactly what you are getting in both the crucial areas of foam quality – weight (number 1) and hardness (number 2). In Australia the lowest density (weight) foam made is 15 kilograms per cubic metre and the average density of foam sold is around 19 kilograms per cubic metre. 30 years ago the average density sold was about 24 kilograms per cubic metre but as price is such an important issue in the Furniture Industry (because of competition internally and imports externally) many manufacturers are using more and more low quality foam.. This is a big pity – however a sign of the times.
The seat of a lounge carries around 80% of a person's weight whilst the back and arms carry the rest (20%). It is logical therefore that if a compromise has to be made it should be on the back foam and arm foams – the less the load carry the less the quality of foam required. Seating foam should be no less than 30kgs per cubic metre as a low weight foam seat, if used every day, will not last. Generally, back foam should be around 45 – 80 in hardness (regardless of the weight) and seat foam around 100 to 140 in hardness and be a minimum of 100mm thick. As the thickness reduces the hardness needs to be increased and also so does the weight.
Foam has an enormous variety of uses. These include furniture & bedding, sporting, transport, packaging, insulation and many others. Foam can also be made in a wide variety of weights and hardness's from around 15/45 through to 50/500 – therefore a foam for every application!!!!!!!
Foam Chemical Process
Flexible Polyurethane Foam is formed by a reaction of liquid chemicals when mixed together. When the chemicals are mixed in the correct proportion they react and expand. Generally the expansion rate is about 40 – 1 (meaning 25mm of the correct chemical mix will expand to about a meter of solid foam). Colour is added to the mix of chemicals at the start of the process so that the different types of foam can be distinguished when being used and sold. If colour wasn't added all the foams would be white – regardless of the foam grade.
There are two basic ways of mixing the chemicals together – one is a line machine and the other is a box machine. The line machine is the "mass production" method where chemicals are mixed and pumped onto a moving conveyer system which allows for long pours to be made – from which, at the end of the conveyer, smaller, more easily usable sized blocks are cut (roughly 2 meters square). The box machine is a single block method where chemicals are mixed and pumped into a box roughly 2 meters square. It is far more cost efficient to make foam on the line machine for major use foams. For specialty grades it is better for the box machine to be used because small quantities can be made.
There are two main chemicals used in the making of foam, namely polyol and TDI. These are mixed with various catalysts, water and blowing agents to cause the required reaction. The mix of these chemicals determines the type of foam that results. From the time the chemicals are mixed together to when they reach the full height of the reaction takes only a few minutes - however the reaction continues to generate heat for several hours after that and reaches its hottest about four hours after the initial reaction. Although the foam can be moved and stored within minutes of forming it cannot be processed for approximately 12 hours. Because colour is an additive which brings no features to the foam other than easy identification, it obviously means that it is not relevant to the performance of the foam. The two things that are important to the performance of foam are WEIGHT (referred to as density) and HARDNESS.