Meant to fill in any space between the head of your penis and the head of the sleeve.  Just measure the amount you need and cut it to size.  Insert into the sleeve before putting it on to provide reinforcement.  Color of insert will vary.  Designed by Vixen Creations to fit the girth/width openings of the inner measurements of the Ride On, Holster, and Colussus (see "details" under each of those products).