Most foam that we use for upholstery has 4 digits. The first two numbers are the density and the next two are the ILD. If the foam is a 1560, that means that it has 1.5 pound density and has and ILD of 60. A 1.5 pound density means that a block of the foam that is a perfect square foot will weigh 1.5 pounds. It the number was a 2860 it would mean that the foam had a density of 2.8 pounds. That means that same square foot block would weight 2.8 pounds. That is almost double the density. The 2.8 lb foam would typically be considered a much high quality.
ILD stands for Indentation Load Deflection. The density is going to tell you how much foam you actually have in a square foot block of that material. The higher the density, the heavier that one square foot block. The other number that is important is ILD. Here you are trying to measure how many pounds of pressure it takes to indent the foam with a standard measure. The higher the number, the better it will resist indentation. The number that really determines quality of the foam is the density. We usually use a density between 1.6 and 2.8 depending on the product. We typically use a ILD of 60. With our higher end bar stools, we also add layers of cotton on top of the foam which totally changes the properties of the seat.
The other factor you want to consider when buying foam or an item made of foam is what type of fire rating does it have. There is fire proof foam, fire resistant foam, and then there is regular foam. Most companies use regular foam unless that product is going into Boston. For Boston, we add a Dacron layer around the seat between the vinyl and the foam. We also have used Code Red foam which is supposed to be fire proof.
Now if you are making your own furniture, you will need to order the foam cut to size or be able to cut it when it arrives. We get almost all of our foam already cut to size because we don't have fast machines for cutting foam like our vendors. There are two main types of foam. There is open cell foam and closed cell foam. Open cell foam is what is used in furniture. The open cells let air escape when you sit on the seat and then return back to its regular shape when you get up. The higher ILD the better the seats ability to reform and resist indentation. This is all kind of complicated and may not be information that you need to know. At least you know that we know about it.
There is even an association that controls foam standards to keep everyone straight. If you want to learn more about foam for furniture, you want to check out the Polyurethane Foam Association. I bet they throw great parties.