Brand: Bell Racing
Rear helmet spoilers combat helmet lift by filling in the area behind the top of the helmet. They are especially effective in open cars with a cowling behind the driver's head. The spoiler smooths the transition between the helmet and the cowling, filling in the low-pressure area.
This clear plastic spoiler adheres to your helmet with double-stick tape (provided) that is strong enough to hold, but not so strong that it will take off paint when removed. The V.06 rear spoiler is designed to fit Bell helmets with a smooth shell with no vent openings in back, but it could probably be made to fit other brands with a little work.
Note: Depending on the size of your helmet, you may need to loosen or tighten the curvature of the spoiler slightly to fit the shell. Warming the plastic by leaving it in the sun for an hour or so will help make it conform.