The development of new solutions to reduce impact of noise receives constant attention both from the research and engineering communities. Even though the proposed systems tend to diversify, multi-layered absorbers based on foams remain the most common. Such structures feature one or several thick slabs of foam and are completed by protective or tuning layers of small thickness inserted between slabs or on the free surface. These layers (acoustics screens or films) bring a number of challenges. Firstly, their thickness makes them hard to characterise and some parameters are uncertain. Secondly, the bonding to the surrounding system alter the effective properties. Given the strong influence the films have on the system's response, it appears important to account for these uncertainties from the design phase on. The present contribution introduces a new technique to efficiently account for uncertainty linked to the screens. More precisely, the proposed approach is based on separating the average film influence from the deviation due to uncertainties. This allows to estimate the response envelope using a pre-computed average response and the properties. The results computed for a range of typical and challenging configurations are promising and validate the robustness of the method at any angle of incidence.