Do you know where Sunshine Kids and Britax might have that info available? I couldn't find anything on the Britax website today.
Maybe I just don't get it about the foam. I felt the Britax Roundabout and Marathon in the store and each felt like they had about a half inch of any padding around the base. I assume this is the EPS/EPP foam, right? How do I know that that little bit of foam will do anything significant? I guess I feel like if I'm gonna bite the bullet on buying a car seat with the energy-absorbing foam I'd go with something like the Boulevard that seems to have LOTS of it. Or am I understanding things wrong?
Without knowing the exact baseline, and without knowing how other companies' seats rank, having the info from Sunshine Kids or Britax wouldn't really make a difference. I know there are some crash test videos out there, but they don't address the foam specifically.
As for the foam, I think you're referring to the comfort foam (it's squishy). The EPP/EPS foam is like styrofoam. You'd have to peel back the cover to see it. It will feel hard, but it absorbs energy in a crash. Like PPs have said, it's the same stuff that's in a bike helmet.
For the record, the Marathon actually has more EPS foam than the Boulevard, because the foam is really only needed around the head. Since the BV has an adjustable headrest, it only has the foam in the headwings, since those will always be around the kid's head. The Marathon has it throughout the seat to ensure that it's next to a kid's head no matter how big/small the kid is. While it certainly can't hurt to have the foam on other parts of the body, it's probably not necessary, either.