Negative pressure wound therapy (NPWT) is the treatment of choice for chronic wounds; yet, it is associated with considerable workload. Prompted by its nonadhesive and wound-healing properties, this study investigated the effect of an additional polymeric membrane interface dressing (PMD; PolyMem WIC) in NPWT. From October 2011 to April 2013, 60 consecutive patients with chronic leg wounds or surgical site infections after revascularization of lower extremities were randomly allocated to either treatment with conventional NPWT (control arm) or NPWT with an additional PMD (intervention arm). The primary outcome was wound healing achieved within 30 days, the secondary endpoints included: number of days between dressing changes, wound-related pain, cost efficiency, and occurrence of adverse events (ClinTrials.gov Identifier: NCT02399722). Forty-seven patients completed follow-up. No difference in wound healing was observed (p > 0.05) between both study arms. The additional PMD allowed significantly longer wearing times (days) between dressing changes (intervention: 8.8 ± 0.5, control: 4.8 ± 0.2; p < 0.001). Pain was slightly higher in patients randomized to NPWT alone (VAS score: 4.8 ± 2.9) compared to NPWT + PMD (VAS score: 3.0 ± 2.9, p = 0.063). No wound infections were observed. Costs were reduced by 34% per patient in the intervention arm. These results suggest that the combination of NPWT and an additional interface PMD is a safe and economic method for the treatment of chronic wounds, which requires significantly fewer dressing changes for a comparable wound healing.