Genuine Arai Replacement Helmet Interior Lining Eco Pure Lining (grey in colour) to Fit: Chaser-V Pro. Rebel. Arai helmet skull pads are the interior comfort pad at the top of interior of an arai helmet, they come in various thickness and also sized according to the shell size. To check the size needed for your helmet, remove the current interior (usually 4 poppers, 1 at each corner, note some older arai helmets did not have removable interiors). The interior has a white tab which will give its thickness in mm, and the shell size in roman numerals.