Any memory foam mattress with a density value below 5 pounds per cubic foot (PCF) falls into the category of low density memory foam.
Low density memory foam layers are softer than the high density layers and are usually used as the upper most top layer of the mattress. The more expensive memory foam mattresses use multiple layers of memory foam. For example, a 3 inch high density memory foam layer with a 2 inch low density memory foam layer on top.
Low density memory foam is usually cheaper than high density memory foam. The open cells are bigger and fewer. This results in a much softer feel as the air in the cells is spread to adjoining cells at a faster rate and so you sink faster than you do with high density foam. Low density memory foam is not as durable as high density and will not last as long. If you need a memory foam bed due to lower back pain in the morning, then you probably will not want a low density memory foam layer on the top.
Whether or not you make a memory foam mattress with two memory foam layers on top – high density followed by a low density, depends mostly on personal preference and your weight. If the total weight of the person or persons sleeping on the memory foam bed will be below 200 pounds, then a low density memory foam layer on top may work out just fine. If the total weight on the mattress will be greater than 200 pounds, then you probably will want only a thick high density layer on top.
This density value can be confirmed by the consumer with two commonly available tools in a household. A bathroom scale and a tape measure.
The measurement and calculation process is the same as demonstrated on the high density memory foam page of this website.
1. Using a tape measure I measured the dimensions of the low density Queen size memory foam layer. It measured 60″x80″x2″ and was supposed to have a density value of 4.5 PCF.
The dimensions were first converted to cubic feet as follows,
60″x80″x2″ = 9,600 cubic inches. And since one cubic foot equals 1,728 cubic inches (12″x12″x12″ = 1,728 cubic inches), the cubic feet of the layer is,
9,600/1,728 = 5.56 cubic feet.
2. I then weighed the memory foam as follows,
I weighed first just myself on the bathroom scale, 165 pounds. Then while holding the memory foam I weighed both myself and the foam, 180 pounds.
The memory foam layer itself weighed: 180 – 165 = 15 pounds.
3. Now just a simple division is required,
15 pounds / 5.56 cubic feet = 2.7 PCF and NOT 4.5 PCF!
Once again, I did not receive what I payed for and quickly demanded the correct replacement.
