Eight years ago I performed the first-ever scientific comparison testing of roll bar padding and published the results in the July 1990 SCR. Back then many racers were still using commercial pipe insulation made from open-cell neoprene foam. They mistakenly thought that was good enough, if they thought about it at all. Most racers were more concerned with the color of their roll bar padding than the level of protection it afforded.
   My testing conclusively proved that pipe insulation was close to useless for protecting the driver's head. The tests also showed that the closed-cell polyethylene roll bar padding offered as an alternative was not much better. I also found that two then-new roll bar paddings made from totally different foam materials were a significant improvement. One was produced by California's Simpson Safety Products. The second, and the best-performing padding tested, was made by a newcomer, Brotherton Supply Company, Inc. (BSCI) of Mooresville, North Carolina.
   Simpson's roll bar padding was made from a polypropylene foam called BeadAll, similar to the BeadAll foam used in their helmet liners. BSCI's padding was made from a modified open-cell polyurethane foam specially formulated to enhance its energy-absorbing properties. The foam was unusual in that it was quite rate-sensitive when compressed. Squeeze the material with your hand and it would slowly yield to the pressure and compress; strike it with a hammer and it would behave as if it was a much stiffer material. In other words, it exhibited viscous damping properties, like very thick oil. The material would also gradually return to its original shape once the pressure was released, which can be important during multiple impacts.
   Visco-elastic foams are nearly ideal for absorbing impact energy. The only variables are how a specific foam is formulated and, of course, how thick the roll bar padding is. But before we get into those details, let's consider what happens during a crash impact.

If you are not sure about your roll bar padding, there are several things to look for. First is the cross-sectional shape. All SFI-certified pads have a crescent shape, not a fully circular cross section. Second is the hardness. If you can squeeze the padding between your thumb and forefinger until it almost bottoms out, it will not protect your head in a hard hit. Third is the padding's chemical resistance. If soaking it overnight in acetone does not deteriorate the foam and turn it into a weak mush, it is probably polyethylene and not very suitable as roll bar padding. (Mike Adaskaveg)

   When a driver's helmeted head strikes a car's roll cage, or any other blunt hard object for that matter, his first line of defense is his helmet. The outer shell is designed to resist penetration and to distribute the impact energy over as great an area of the liner as possible. In addition to absorbing energy, the helmet liner must minimize the acceleration of the skull. It does this by crushing gradually and avoiding a rapid rebound. If the foam springs back too fast, it can actually amplify the acceleration.
   Energy not absorbed by a helmet lining will go into accelerating the skull, and then the brain. The greater the acceleration of the skull, the greater the risk of brain damage caused by its impact with the inside of the skull. Closed-head brain injuries are simply the result of high skull accelerations that resulted in brain impacts with the skull.
   The medical community has done a great deal of research into brain damage resulting from blunt-object trauma, or blows to the head that do not penetrate the skull. Without going into the gory details, it helps to understand a couple of things. The greater the rate of the brain's acceleration, the more dangerous it is. (See Figure 1.)
   Accelerations of the brain less than about 50 G's are rarely fatal, even if they last for 0.1 seconds, while accelerations exceeding several hundred G's are almost always fatal, even if they last for only 0.001 seconds. To lessen the danger, it is best if a blow to the head can be cushioned enough to limit the acceleration of your brain to less than 50 G's.
   But there is more to the problem. Blows to the head rarely produce accelerations of a rate and duration comparable to the concussion-tolerance curve shown in Figure 1. Instead, they usually produce an acceleration profile whose rate changes very rapidly over the short duration of the impact. These complex changes need to be averaged in a way that gives greater weight to the higher acceleration peaks than the lower, longer-lasting brain acceleration components.
   One way to do this is through the Gadd Severity Index, or GSI. I won't go into the mathematical details of the GSI, but I will say that a GSI value of 1500 is widely accepted as the maximum limit for blunt-object blows to the head that will not result in brain damage. As a racer, that's your bottom line.
   Modern racing crash helmets do an excellent job of protecting a driver's skull from excessive accelerations during low to moderate impacts. But as the severity of the impact increases, it becomes increasingly difficult for a helmet to protect the brain.
   Simply put, additional protection becomes necessary as the severity of impact increases. That's where roll bar padding comes in. The greater the total thickness of padding available to cushion a blow to the head, the lower the brain's accelerations will be. But, again, it is not only the thickness of the foam that is important, it is also the choice of material.
   Shortly after my 1990 test results were published, the U.S. Auto Club approached the SFI Foundation and requested a series of independent tests of roll bar padding materials with the idea of developing a specification. The specification was to include impact testing procedures and performance limits, as well as a fire resistance requirement.
   SFI commissioned the University of Southern California's Head Research Protection Lab to perform the initial tests, which they did with an apparatus similar to the one used to evaluate crash helmets. Their tests, conducted on 15 different samples of commonly available roll bar pads, yielded results very similar to mine. The report to SFI concluded that "analysis of the impact data shows that the majority of products used as roll cage protective padding have little or no energy absorbing capabilities. … Roll cage padding configurations showed peak headform accelerations approximately equal to the peak headform acceleration of an impact without any type of roll cage padding."
   The USC testing also showed that two companies were producing roll cage pads made from fundamentally different materials which were much firmer than conventional wisdom would indicate. The two companies? Simpson Safety and BSCI, the same ones I had cited years before as makers of superior padding.

These two sticks of energy-absorbing polyurethane foam padding conform to SFI specifications. Instead of being continuously extruded into a tube the way polyethylene foam padding is made, these have been individually cast. The unlabeled piece is from Simpson/BSR. (Mike Adaskaveg)

   SFI then combined USC's padding test results with other data that they had from helmet research and some of the medical industry's research into concussions and developed a specification for roll cage padding. SFI Specification 45.1 for Roll Cage Padding, released in 1995, was the result. USAC then adopted that specification and added it to their rulebooks, although enforcement of the requirement has been sadly lacking.
   The SFI roll bar padding test procedure is similar to the test used for evaluating crash helmets, although for these tests the headform that impacts the padding is not protected by a helmet. The accelerations of the headform are directly measured, and only the roll bar padding is evaluated in the test. Obviously, during actual crash impacts, the driver's helmet provides additional protection.
   The testing consists of three successive impacts by an 11-pound aluminum DOT headform traveling at 14.5 feet per second (approx. 10 m.p.h.), all at the same point on the padding. To pass the test, the acceleration may not exceed 200 G's for the first impact and 250 G's for the following two impacts. In addition, the calculated Gadd Severity Index can not exceed 1500 for any of the impacts.
   Since many of the energy-absorbing polyurethane foams decrease in firmness with increasing temperature, the roll bar padding materials are required to pass the impact tests at 70°F and at 110°F. Finally, the materials are required to self-extinguish within 10 seconds following exposure to an open propane flame, and to do so without melting or dripping.

To be certain that your roll bar padding conforms to SFI specifications, look for this sticker on the inside. (Mike Adaskaveg)

   Since their introduction three years ago, only four manufacturers have submitted roll bar pads that have passed the SFI tests. They are BSCI, JAZ Products, Simpson Race Products, and Taylor Motorsports Products.
   According to SFI president Arnie Kuhns, none of the popular offset-center roll bar pads made from polyethylene foam stand a chance of passing the tests. That also means they will not offer you much protection.
    Polyethylene foam pads feel like they would cushion a blow, and they will—provided the blow is slight to moderate. But if you hit your head against a roll bar hard enough to cause possible brain damage, polyethylene foam padding will not help you. The cells within the foam will simply rupture, and it will crush to nearly nothing. To see for yourself, hit your polyethylene-foam-padded roll cage with a baseball bat. Light taps with the bat will bounce off the foam, but hard blows will go right through it to the steel tubing. Your head would do the same.
   Roll bar pads that pass the SFI Specification feel too hard to cushion a blow, but they need to be that firm to absorb the higher-energy impacts associated with head injuries.
   All four manufacturers who have passed the tests did so with pads made from similar modified polyurethane foam materials. The Simpson BeadAll roll bar padding that performed well in my tests as well as USC's is no longer in production. Instead, Simpson has teamed with BSR and Reb-Co to produce padding made from a polyurethane foam similar to BSCI's original product. BSR and Reb-Co each offer the same padding for sale directly, but of those three sources, only the padding offered by Simpson has been SFI certified.
   JAZ Products offers padding in three different thicknesses ranging from 1/2" to 1". While each thickness passes the SFI test limits, the results of those tests reveal the importance of padding thickness when it comes to reducing peak head accelerations. (See Table 1.)
Table 1. Peak Headform Acceleration in G's.
  Test at 70°F  Test at 110°F

Pad	1st	3rd	1st	3rd
Thickness	Impact	Impact	Impact	Impact
1/2"	139	164	147	170
3/4"	93	124	111	136
1"	74	88	74	89

c
    

     It is clear from this data that thicker roll bar padding dramatically reduces head accelerations and therefore the risk of brain injury in severe head impacts.
   That brings us to my final point. Roll bar padding is no place to scrimp on materials. The padding materials that can pass the SFI Specification 45.1 tests are more expensive than lesser materials, but they are also dramatically superior in performance. The difference is as dramatic as wearing a cotton T-shirt and jeans instead of a triple-layer firesuit with Nomex underwear. And we know you'd never do that.

SFI Certified Roll Bar Padding Sources:
Brotherton Supply Company, Inc. (BSCI)
P.O. Box 1203
Mooresville, NC 28115
704/664-3005

JAZ Products
1212 East Santa Paula Street
Santa Paula, CA 93060
805/525-8800

Simpson Race Products/ BSR Products
7701 North Tryon Street
Charlotte, NC 28262
704/547-0901

Taylor Motorsports Products
1255 North Tustin Avenue
Anaheim, CA 92807
714/630-7850

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