Bayer Leverkusen Onesie. Celebrate the long and rich history of Bayer Leverkusen with this authentic club onesie. Start 'em early and they'll love Bayer for life. Cotton. NOTE: The logo on this tee is distressed; it's meant to look weathered. This product was pretreated to ensure quality and long life-span of the graphic. Please wash and dry before first wearing to remove any residue that may be visible.