Physical energy barriers blocked solid matter and could be used defensively as force fields. A physical energy barrier was used by the Silurians to trap the occupants of Cwmtaff within itself. It was invisible to the naked eye, but could be seen if it was hit, or when excited by the Doctor's sonic screwdriver. The barrier was red in colour and did not allow people pass through it. It did, however, allow rain to pass through. It could also block out light, making it seem as though it was night. (TV: The Hungry Earth)