OK, even dumber question... What is the zipper for then?
According to Mister 4x4, the possibilities are endless!........This pause gives everyone time to reminisce!
As posted by 72conv, unzipping the rear glass (Ford's official name for this part is "Window, Folding Top Back Curtain") created a sort of breezeway. On those scorching summer days, when the sun beat down and you had a non-A/C vert, lowering the rear"Curtain" was like inviting a cool, refreshing breeze into your car. A "Breezeway" option was available on the '63-66 Full-size Mercury, where the center section of a near vertical rear glass would retract into the trunk, creating a flow-through ventilation, a true breezeway.
This type of window was initially available on '57-58 MercuryTurnpike Cruisers and '58-60 Mark Series Lincolns. As A/C systems improved and convertibles were available in all Ford/Lincoln-Mercury vehicle lines, the Breezeway rear window quickly disappeared from the option sheets. A modified version was available on the '67-68 full-size Mercury, but it didn't have many takers, so it was discontinued and took its final curtain call at the end of the '68 model year.
Another reason had to do with service replacement costs. A new Ford convertible top did not include the rear glass (Curtain). If you needed a new rear curtain and not the top, you were not forced to purchase a more expensive top and glass together. Before the rear curtain/glass was discontinued on 11/81, the retail price was $151.50 (approx 538.49 in 2024 dollars). When discontinued, the retail price of the convertible top was $310.56 (approx 1,103.86 in 2024 dollars). So the money saved added up if you didn't need both parts.
Now you know more about breezeways than you ever thought you would need to know!