Architecting a System of Systems (SoS) is a complex task. Capabilities of heterogeneous and interactive sub-systems are composed to fulfil a mission, while preserving, as possible, the autonomy, independence, geographic distribution… of sub-systems and to face up efficiently while remaining as resilient as possible to disturbances and emergent phenomenon. The “-ilities” are relevant non-functional abilities (e.g. robustness, resilience, flexibility, adaptability, survivability, interoperability…) for guiding SoS architects and managers to choose and interface sub-systems. The goal is to become able to increase or decrease the value of these “–ilities” thanks to their interest for the SoS mission. The here presented work aims to support resilient SoS design and, in particular, their architecting by proposing a formalised model of property allowing to define and describe an “–ility” and a behavioural modelling approach to evaluate it.