2 pieces of plexiglass with vent holes.  Real glass should be on the outside (front of the door).  One piece of plexiglass is for the middle and the other for the inside so that if the door is let go before the bottle is all the way out it won't break the glass. For Cavalier bottle doors that have outside dimensions of 37-3/8 x 5-5/8.  It is important to check these measurements.   ***RP37 gasket is sold separately.  Requires 15'.