From page 20 in the Riders Manual:
" Leather or textile riding suits (i.e., Cordura, Kevlar, or Aerostich-type).
No textile suits will be allowed in the Advanced group. Two-piece
suits must zip together; full circumference is required.
Airmesh-style suits (where you can see your skin through
them) will NOT be permitted.
o No jeans allowed. Rental leathers are available."