A healer believes wearing silk prevents transmission of energy through the silk, so it could be protective in shielding empaths from getting overwhelmed. Is this correct?

This is not correct. It is a misinterpretation of the energetics involved here. This is not acting as a shield, it is that the silk itself has energy and a consciousness, and so that is being perceived as an energetic layer and so the overall impression is one of greater density, and this is then assumed to represent a barrier. It is simply the presence of the consciousness being more pronounced than with other cloth materials and this does not restrict other consciousness from going to and fro and impinging on the individual through the usual means of perception. There are many, many energetic layers around a person and within them—all of which are penetrable by consciousness of all kinds except for the need for safety creating a barrier when from a negative source—but that is a purposeful energetic construct. That is not what is taking place here. That is not to say the energy of the silk cannot be trained in the way of a crystal to do something of value, but it will not be able to prevent the penetration of outside consciousness. It could be used as a sentinel in the same way as a quartz crystal, but on its own, in a passive mode, it will not be a safety barrier.