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 which 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 things. Let's look at those two critical factors:-
The weight of foam is measured by kilograms per cubic meter. A block of foam measuring 1 meter x 1 meter x 1 meter (a cubic meter) is weighed and the weight registered becomes the first part of the code. For example if a cubic meter of a particular type of foam is weighed and it weighs 23 kilograms then the first part of its code is 23. If it weighed 15 kilograms then the first part of the code would be 15. And so on across all the different foams.
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. As an average, a middle hardness foam requires 130 Newton's of force to compress it to 40% of it's height at 100mm. 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 100 then the second part of the code is 100, if it is 40 then the second part is 40 – and so on.
By adding the two measurements (weight and force) together the code is complete. A foam that weighs 23 kilograms per cubic meter and requires a force of 130 Newton 's to compress it to 40% of its original height therefore has a code of 23/130. A foam that weighs 15 kilograms per cubic meter and requires a force of 100 Newton 's to compress it to 40% of its original height therefore has a code of 15/100. A foam that weighs 35 kilograms per cubic meter and requires a force of 130 Newton 's to compress it to 40% of its original height therefore has a code of 35/130. A foam that weighs 15 kilograms per cubic meter and requires a force of 60 Newton 's to compress it to 40% of its original height therefore has a code of 15/60. A foam that weighs 25 kilograms per cubic meter and requires a force of 60 Newton 's to compress it to 40% of its original height therefore has a code of 25/60. And so on. (note 23/130 & 35/130 have the same hardness but 23/130 weighs much, much 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. Similarly the 25/60 & 15/60).
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 meter and the average density of foam sold is around 19 kilograms per cubic meter. Because 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. (Fifteen years ago the average density sold was about 24 kilograms per cubic meter – today it is 19 kilograms per cubic meter). This is a big pity – however a sign of the times. If a compromise has to be made on quality in a lounge it should not be on the seating.
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 weight of foam required. Seating foam should be no less than 30 kgs per cubic metre - however we are in a position where we supply to demand and at certain price points. The result of this is that much seating foam used is far less in weight than 30 kgs/M 3. Low density seating if used everyday not only will not last but cannot 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 increasedand also (generally) 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!!!!!!! Just remember that weight is quality.High weight foams (even of low hardness) last longer than low weight foams (even of high hardness) under the same usage. As a general rule of "thumb" if you had two foams of the SAME hardness but one was (say) 35 Kgs/M3 and the other was (say) 15 Kgs/M3, the heavier foam would deteriorate by 10% in the first year and the lighter foam would deteriorate by over 50% - that is the difference. Weight is quality – not hardness. Choose wisely – choose heavy.
Foam Chemical Process
Flexible Polyurethane Foam (foam) is formed by a reaction of liquid chemicals when mixed together. Similar to the making of bread, when the ingredients (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 – or in the old scale 1 inch makes 40 inches). Colour is added to the mix of chemicals at the start of the process so that the different types/densities can be distinguished when being used and sold. If colour wasn't added all the foams would be white – regardless of density/type.
There are two basic ways of mixing the chemicals together – one is a line machine and the other is a box machine. The line machineis 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 machineis 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 it's 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.