Apex overlay markers are used for short term delineation of travel lanes, usually during paving projects.  Each marker has a butyl rubber adhesive strip and a narrow band of reflective material.  White markers are reflective only on one side, with two side reflectivity applied to the yellow markers.  Traffic Supply, Inc. also stocks these markers with a clear plastic cover for use on sealing projects.  Under most conditions,  these markers will have a useful life of about one week.