Developing variant-rich software systems through the application of the software product line approach requires the management of a wide set of requirements. However, in most cases, the focus of those requirements is limited to the functional requirements. The non-functional requirements are often informally defined and their management does not provide traceability mechanisms for their validation. In this paper, we present a multimodel approach that allows the explicit representation of non-functional requirements for software product lines both at domain engineering, and application engineering levels. The multimodel allows the representation of different viewpoints of a software product line, including the non-functional requirements and the relationships that these non-functional requirements might have with features and functionalities. The feasibility of this approach is illustrated through a specific example from the automotive domain.