The Census Bureau conducted the 2017 Pressure Seal Mailing Materials Test to evaluate the impact of replacing some letters and postcards in the ACS mail materials with pressure seal mailers. Since a pressure seal mailer costs less than a letter with an envelope, the Census Bureau could realize some cost savings by replacing a letter with a pressure seal mailer, as long as the mailer does not negatively impact response rates. When compared to a postcard, a pressure seal mailer costs more than a postcard. However, a pressure seal mailer has the added benefit of being able to conceal personal information, such as an internet user ID, which could help encourage internet response. An increase in internet response would reduce the more costly phases of nonresponse followup and could therefore potentially decrease overall production costs. This research paper summarizes the results from the pressure seal mailing materials test, which took place using randomly selected cases from the May 2017 ACS production sample and assigning them one of three experimental treatments or a control group.