Last year Delmer Teet and Ron Conlon made up two of these simple devices to block the wind that whips from behind the driver at highway speeds. Here is an update on their effectiveness and plans to make your own.
The materials are 1/4" plexiglass or lexan and some straps. These I found hiding in the garage from old projects but they are not expensive. Lexan is harder and scratch resistant but the plexiglass polishes well. The tools were a hacksaw, drill and file.
Dimensions are 36"x12" with rounded corners to taste.
Seatbelt notches are 1"x 3".
Mounting holes or slots are 3" from the edge (not the seatbelt slot which would be 2") spaced 6" apart and 1.5 inches from the lower edge. More than 12" above the seat back (not headrest) will get too close to the top mechanism and lower than 10" will muss your hair.
Comments on these are from using one for a year. It works well to keep a hat on and cut down on wind buffeting. It is all but invisible. With the windows down, side draughts will still take a hat particularly at intermediate speeds ­ 30 to 45 mph ­ or when a big rig passes in the other direction.With the mount on the seat, you will feel an occasional push from behind as a gust hits it. In just the correct angle of sun, it will reflect straight ahead and into your mirror. This happens only at dawn and dusk. The straps mean I can easily remove the windbreak for town driving. This prevents scratching from stuff being tossed in the back and eases top operation from the seat. The seats can still be adjusted but can make the top edge look slanted if they are too different. I usually balance the look. The rearview mirror use is as normal. There is a lot of wind now from between the two seats under the windbreak, which is fine in summer but tends to lift my full rim hat above 70mph. So I added a flap of heavy material between the seats hanging from the windbreak to address this. The straps are horizontal but could be placed on the vertical to wrap the headrest itself. The plexiglass could be a lighter grade but heavier is not going to help anything.
There are alternatives to this approach. A screen material like the plastic bug screens will work if stretched across a roll bar. Certain types of car shades will do a good job inexpensively. There is a net bag that covers both headrests and or seats. I have seen one of these on a Bimmer that looked awful but looks can be fixed and old pantyhose would have been better looking on this car. Pantyhose works, by the way, if you cut the legs and crotch out and pull it over the two seats and headrests. It comes in appropriate colors but the teller won't believe you if you tell 'em what it is for. So don't try.