triple bolster rear seat
 

I am planning on having some triple bolsters made for my back seat and have a few questions.
1. Are the arm rests made out of just a firm foam or is there a solid center? if there is a solid piece, what is it made of?

2. I am going to make the seat 15 to 16 inches wide in the back where your but is and about 11 to 12 inches in the front to help hold you in. How far out does the seat stay narrow before going wide in the back? Any help would be great. I think the design of the triple bolster is awesome and will be great for the kids.

Thank you in advance.
Mark