A Teflon bullet was a type of ammunition used by Torchwood Three.
The bullet was made from an alien alloy, and their noses were hollowed out and filled with a Teflon fluid. A victim of the bullets would have an entry wound the size of a penny piece and an exit wound the size of a dinner plate. The Torchwood team used them when facing Weevils. (PROSE: Slow Decay)