Abstract Survey researchers are continually evaluating approaches to increase response rates, especially those that can be implemented with little or no costs. In this study, we experimentally evaluated whether or not including Quick Response (QR) codes in mailed recruitment materials for self-administered web surveys increased web survey participation. We also assessed whether mailing these materials in a non-standard envelope size (6 × 9 inch) yielded a higher response rate than invitations mailed in a standard, #10 envelope (4.125 × 9.5 inch). These experiments were embedded in a sequential mixed-mode (dual-frame phone and web) statewide survey. Including a QR code (in addition to a URL) significantly increased the response rate compared to invitations that only included a URL in our study. As expected, a consequence of including the QR code was an elevated number of completions on smartphones or tablets among households randomly assigned to the QR code condition. The use of a larger (6 × 9 inch) envelope did not affect the overall response rate but did significantly boost the response rate for the landline sample (envelopes addressed to “STATE resident”) while having little effect for the wireless sample (envelopes addressed by name). This study suggests that incorporating both QR codes and larger (6 × 9 inch) envelopes in mail recruitment materials for web surveys is a cost-effective approach to increase web participation.