In order to understand how memory foam works it can be necessary to understand how we think about it when we are designing a new mattress. All memory foam mattresses, whether it is very soft or very firm, follow the same basic logic. Memory foam itself is very soft but it is also very body conforming, which means it readily molds to the contours of your body. Ideally, you would like your spine to be in its proper alignment, which is not the same as wanting your spine to be straight. Humans are not shaped like that. Traditional innerspring mattresses, on the other hand, can not, by their nature, conform to the shape of a human spine since they are made of steel. The whole purpose of the memory foam layer is to allow your spine (and the rest of you) to relax into a totally natural position.
Below the memory foam are a number of more traditional polyurethane foam layers, which is where your support comes from. That is what you will be resting on when you sink through the memory foam layer. Some mattresses, like The Outback, are only two layers. That keeps the cost of the mattress down while still providing many of the benefits found in any well made memory foam mattress. Others, like The Summit and the Oasis, have several layers, adding what we call “transition layers” in between the memory foam and the base foam. The purpose of these extra layers is to eliminate the feeling of “bottoming out.”