Sometimes you see an eggcrate layer (convoluted) in a memory foam mattress and sometimes you do not. The idea is to allow some air ventilation between the bottom layers of conventional foam and the top layers of memory foam. Most of the high-end memory foam mattresses have this feature.
Like the bottom base layer this layer also needs to have a high IFD value since it is part of the lower support.
This layer only needs to be about 2 1/2 inches thick. Typical desired specifications you should look for are,
Density: somewhere around 2 PCF.
IFD: 40 – 50.
