They were an inflatable that fit over the existing hard shell helmet. We had some pretty aggressive players that had there bell rung a few times and after one parent bought them a few other did as well. They minimize the force to the head from contact, the fear was that they don't slip as easily as a smooth plastic surface of a shell. We never had problems with neck injuries due to them catching but I can see why there would be concern. We had players use them for about four straight years and I would say we definitely saw a decrease in concussions/concussion like symptoms.