So there's several different ways to create diaper cakes and all of them are effective in getting the "cake" feel.
Here's what I use to create custom diaper cakes.
Newborn diapers. The smaller size of these diapers create the perfect height for the cake layers
Pampers. I personally like the Pampers Swaddle Newborn diapers. What I like about these is that they are soft to the touch and also the outside is all white and creates a better "cake" feel.
Close up of the Pampers Newborn diaper. The yellow band at the top gives me a good guide for lining up the diapers and allows me to have an all white cake.
As I said, there's several ways to put together a diaper cake. This is how I create them, starting with one and then creating a continuous roll of diapers, all held together with first aid tape.
What is needed to start the process. Newborn diapers and First Aid tape
Johnson and Johnson First Aid tape. This is used to hold the diapers together, and while the tape will be on the diapers, all diapers are still usable once the tape is removed
The rolling of the diapers. It's one continuous roll, creating the cake "layers"