Not a helmet. Made from a steel mesh and kevlar bib, a mask protects your face, head and neck from being hit by a fencing weapon.
There are 3 different types of masks depending on what weapon you choose to fence. There are a couple of key difference to note about these.
Foil
The foil mask has an insulated mesh with a metallic lame that covers 3/4 of the bib. This is because the neck is valid target in foil where the head up neck are not. When any part other than the lame is hit, a non-valid light will display.
Sabre
The sabre mask has an un-insulated mesh with a full lame of the bib. The entire head and neck are a valid target. The blade of the sabre is conductive so when the mask is a hit, a on target (coloured) light will register.
Epee
The epee mask is fully insulated with no lame material on it at all. The whole body is target in epee, including the feet. This means that the electronics on the weapon work different from foil or sabre. Both of these weapons work by conducting on a lame (un-insulated surface) to register a valid hit on target).
Hutt Valley Fencing Club 