To upgrade or downgrade the lining of your Arai helmet, you can order the lining in different strengths. Please, take the standard strengths of your helmet from the following table: Head circumference in cm Helmet size Tighten Standard Looser 54 XS 3.5cm 30 mm 25 mm 20 mm 15 mm 55-56 S 3.5cm 30 mm 25 mm 20 mm 15 mm 12 mm 57-58 M 3.5cm 30 mm 25 mm 20 mm 15 mm 12 mm 59-60 L 3.5cm 30 mm 25 mm 20 mm 15 mm 12 mm 61-62 XL 3.5cm 30 mm 25 mm 20 mm 15 mm 12 mm 63-64 XXL 30 mm 25 mm 20 mm 15 mm 12 mm for Tour-X 4 100% polyester easily cleaned