The seats are 4" the backs are 2" because the table top when in the lower position is higher than the platform for the seat. It is pretty comfortable, however we rarely use it - mostly just for my young nephew who could sleep anywhere.
At our '56 Safari dinette, we made it differently and the table top is the same height as the seat platform so all the foam is 4". I don't have a website page set-up for our '56 Safari dinette, but you can see it in our "It's a Girl!!!
" thread....I will be posting more pictures there soon as we finish up the cabinets this weekend.