More and more software systems are now made of multiple collaborating third-party components. Enabling fine-grained control over the communication between components becomes a major requirement. While software isolation has been studied for a long time in operating systems (OS), most programming languages lack support for isolation. In this context we explore the notion of proxy. A proxy is a surrogate for another object that controls access to this object. We are particularly interested in generic proxy implementations based on language-level reflection. We present an analysis that shows how these reflective proxies can propagate a security policy thanks to the transitive wrapping mechanism. We present a prototype implementation that support transitive wrapping and allows a fine-grained control over an isolated object graph.