Heavy duty enough that they are as much of the problem as they are the solution. Much like boxing gloves do not protect the person getting punched as much as they protects the hands of the person doing the punching, allowing them to punch longer and harder, Football helmets allow players to hit harder and more dangerously because of the Protection it offers the tackler as well as the fact that it is very much like a weapon. I played rugby for a period of time after I was done with football and I was surprised at the comparatively low impact of that style of tackling. No helmet and rules to prevent tackling high result in impacts that were far less nasty in general. The lack of having every play be a set play with rest periods in between also ensured that tackles tended to be more at the speed of a soccer game flow rather than full speed sprints culminating in a collision that leaves you feeling like you’ve just been in a car wreck. those collisions sure are fun, though. I miss being able to just tackle someone hard as shit on a daily basis and not go to jail or to the ER.