The dream can be seen as an outlet for the unconscious mind to express itself. In this case, the foil represents a protective barrier of sorts that we are building up against a conflict or situation that is hard to confront in waking life.
It is possible that your subconscious is trying to protect you from feeling some kind of emotional pain, but this foil could also symbolize the need for some kind of protection or safety.
In any case, the dream is explicitly telling you about your own defense mechanisms and how you cope with difficult situations. It may also signify the need for defensive actions against someone who is trying to harm you.