Kevlar carbon fibre helmets are strong and durable. However, they do crack and break under extreme circumstances. A damaged Kevlar helmet isn't ruined; the damage is repairable. Only a few ingredients are required and the process doesn't take a lot of time. If a helmet owner is patient with the process and careful with detail, a repair will solidify the structural integrity of the helmet with little to no cosmetic scarring. A sportsman can safely use the helmet again.
Remove the padding from inside the helmet. Grind out the damaged area on the helmet. Set the grinder on its side and grind a hole through the centre of the damaged Kevlar. Grind toward the edges of the damaged area from the centre of the hole. Grind away all cracked or broken Kevlar. Make the hole symmetrical.
Sand a 2-inch perimeter around the hole in your helmet on both the inside and outside of the helmet. Sand the entire exterior of the helmet if you plan to repaint your helmet. Cut a piece of Kevlar cloth three inches larger than the circumference of the hole. Tape the cloth over the hole on the inside of the helmet.
Mix the resin and hardener in the bowl at the ratio recommended by the manufacturer. Dip the paint brush into the mixture and dab the Kevlar cloth around the hole. Don't brush the cloth as it will stretch and tear. Saturate the cloth around the hole only. If you dab the Kevlar spanning across the hole, it will sink in and you won't be to add additional layers. Allow the resin to dry for three hours, then dab and saturate the cloth spanning the hole. Turn the helmet over and make sure the cloth is not filling the hole; it should be resting below the hole a fraction of an inch. Allow the resin to cure for three hours.
Cut out resin cloth patches with the same dimensions as the hole. Place a patch in the hole and rest it on top of the first layer of Kevlar. Saturate the cloth and allow it to cure for an hour. Add another layer, allow it to cure, then add another.
Add layers and allow each to cure individually until the patch is above the surface of the helmet's exterior. Sand the patch until it is flush with the surface of the helmet. Replace the padding on the inside of the helmet. The helmet is ready to paint.