Faq II: Equipment & Maintenance:

2.2 Masks

     Foil masks should be well-insulated to prevent touches to the
     head from conducting to the lame' and registering as a touch.
     Electric sabre masks must be conductive, on the other hand, to
     allow head touches.  Epee masks should have bibs that cover the
     collar bones, while foil masks should not descend below the
     collar bones.

     Masks usually come in 3 or 5 sizes, depending on the
     manufacturer.  When sizes are numbered, 5 is usually the largest.
     Sizes are often indicated by the position of a metal tag or rivet
     on the rear portion of the mesh.

     Masks must pass a 12 kg punch test to be certified for
     competition.  Consider subjecting a used mask to such a test
     before using/purchasing it.  Older masks can have smaller bibs
     and weaker mesh (rated to 7 kg), making them less safe.  When
     punch testing a mask, depress the punch perpendicular to the mesh
     without wiggling it.  Do not apply more than the required amount
     of pressure.  Pay particular attention to parts of the mesh that
     have already been dented or bent, including the center crease
     line.  Unnatural dents in the mesh can and should be pushed or
     hammered out.

     The best masks have FIE homologated bibs to protect the throat,
     and are required in high-level competition.  1600N bibs are
     standard in FIE competition for the 1995/96 season.  The CFF
     requires 800N bibs as a minimum in elite competition, while the
     USFA has no FIE bib requirement.

     As of October 1, 1995, the bib is part of the valid foil target.
     Enforcement of this rule at first should only be expected at
     high-level international competitions.  The CFF and USFA have no
     immediate plans to implement this rule.  It is not clear at
     present just how equipment manufacturers will handle this change.
     Metallic sleeves for the bibs of older masks will probably become
     available, attached with velcro or something similar.