Virtualization is emerging as a key mechanism of scaling the infrastructure and facilitating service deployment for future Internet. Network virtualization provides the ability to slice larger, underutilized physical nodes into smaller, virtual ones. To ensure deterministic performance, guaranteed QoS, and independent behavior, virtual nodes have to be properly isolated. However, a high isolation can have an important impact on the node performance and configuration flexibility. This paper investigates the problem of isolation between the slices of a virtualized switch. Our approach consists on adapting isolation to the desired performance and flexibility while ensuring fairness between the slice. Based on that approach, we developed a model that provide the choice between several levels of isolation. Each level corresponds to one or more resources. We implemented this model for a virtualized Open Flow 1.1 switch. We propose a utility-based evaluation balancing performance and flexibility that provide the adapted isolation level to the required demand. This model gives preference to the user to have isolation with a higher flexibility or lower overhead. Our analysis also shows that the overhead and the resource consumption of the isolation is reduced while remaining flexible and dynamic.