The density is never to be overlooked when interested in a memory foam mattress. It is directly responsible for the firmness. In fact, it is more important than the actual thickness. This element is measured in pounds. A higher density means a denser unit and way more firmness. If you are not sure what you need or you do not have any special requirements (like extremely firm or extra soft), you should hunt a memory foam mattress whose density floats around three or four pounds. A five pound density is indicated to those who require extra firmness. Check wakeupinabetterway.org for more info.