When experts test the safety of modern cars, there's no getting around the big, dramatic test: Smashing a car right into a wall, watching it crumple in slow motion, and seeing if the poor crash test dummy inside lives to tell the tale. Thanks to the evolution of seatbelts and airbag, that crash test dummy is less likely to introduce his face to the steering wheel or windshield. Football helmets, it turns out, are tested almost exactly the same way--the helmets are violently smacked against a hard metal surface, and the impact is measured in a lab. According to a brand new study published in the Journal of Neurosurgery, modern football helmets actually reduce the risk of a concussion by 45 to 96 percent compared to the old leather helmets you've seen in old-timey sports reels.

Modern plastic football helmets, then, are football's equivalent of the airbag. Except the issue isn't quite so cut-and-dry--in 2011, a similar impact study declared that plastic football helmets are often no better than leather ones. Concussions and brain injuries are serious problems in football. They can leave permanent damage. The issue is so serious, the United States Congress even introduced two bills in 2011 to ensure children in sports programs were equipped with the proper safety gear.

So who's right? Are helmets actually reducing the risk of concussion, or is it simply impossible to prevent the brain from hammering against the inside of the skull?

Virginia Tech, which carried out the new study, measured front, side, rear, and top-of-head impacts with 10 plastic helmets and two old leather models. Sensors inside a dummy head (poor guys always get the violent jobs) measured the impact from a variety of drop heights, ranging from 1 to 5 feet. In the past, Virginia Tech has used the same system to assign a safety rating to football helmets.

In this test, they found some expected variation in how the 10 plastic helmets performed, but they all did better than the leather helmets of old:

"The leather helmet group had a substantially greater average peak acceleration associated with each drop height compared with modern helmets," says the study. At the 12-inch drop height, modern helmets provided a 59%–63% reduction in peak head acceleration when compared with leather helmets. At the 36-inch drop height, modern helmets provided a 67%–73% reduction in peak head acceleration when compared with leather helmets."

Virginia Tech's experts also addressed the study from 2011, which had found no advantage in plastic helmets over leather ones. They argue that the testing methodology used in the older study didn't accurately represent the kinds of impacts in football games. In that test, a plastic football helmet and a leather helmet were smashed into each other. Not only were the impact speeds too slow, they argued, but in the test, the plastic helmet's padding was absorbing and transferring some of the energy away from the leather helmet. It wasn't an accurate representation of a leather helmet's ability to slow head acceleration.

It's a controversial topic, and as an editorial published in the Neuroscience Journal points out, the older study more closely emulates the on-field conditions of players smashing into each other. The new study doesn't take into account neck movement or other sorts of trauma. So it's likely true that plastic helmets are safer than leather ones, as the drop tests showed, but even the best helmets won't be able to prevent concussions in a real football game.