Spaz Stix Ultimate Black Backer is required when using Mirror Chrome to achieve the full reflective properties of the chrome. Not only will it give your Mirror Chrome the maximum shine, but it seals and protects. Without this backer, Mirror Chrome will not be durable, and will wipe off easily. When used on "external" applications or surfaces other than polycarbonate, use Ultimate Black Backer as a base coat before applying Mirror Chrome. In this scenario, the chrome will require a clear coat.