These helmets all appear to be of more or less equal size. This means that the "additional protection" against skull fracture in the tests is simply from more closely controlled foam inflation.

This implies that most Styrofoam is perhaps a bit too soft and hence they have to add a bit more material to meet the various tests standards.

So if you control the manufacturing process for the foam you actually make is denser and while it is more effective in the tests which are designed to prevent skull fracture they are actually a more dangerous helmet having less protection again concussion.

This is the problem with the people that are working with helmets. Too many of them do not understand the medical problems and others are amateur engineers. Specialized certainly doesn't have any amateur engineers but the medical knowledge of what the actual problems are for a helmet is missing. Therefore they have spot-on made a perfect foam to pass the standards while in fact making the helmet less protective.

Trek has turned this on its head. Their helmets meet but apparently do not exceed the standards for skull fracture while vastly improving the initial deceleration of the head form to the point where concussions are greatly reduced. This will force other manufacturers to come up with other means by which to obtain the same results.

Be aware that children's brains are FAR more susceptible to concussion and hence have to have helmet specifically designed for them. And presently they are not.