I have tried the plexiglass, did not work well. There was a thread posted about 5 months ago, also on the Backdraft site, about a windbreak using fine wire mish with 11/2 inch webbing around it to maintain shape, then using velcro to attach it to each roll bar. I tried it and also added a piece between the bars, the whole system works ok. If you have plexiglass side windows up, it work much better.
