I saw an old Nerf football with the whistles on the side once. It got hung up in a storm drain during hurricane Irene and was completely waterlogged. I had to pass on it though cuse I don't eat gutter water.
On the older, non-silicone CPR models, the foam has the exact same texture as these nerf balls. How do I know? Because one of the idiots in the CPR class decided he was a real man and real men go after foam CPR model tits.