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So, this is going to be a multi part question.
How much weight can I expect to save in a Civic be using Lexan Windows?
What's the difference between the Lexan sold for race car windows and the plexiglass stuff they sell at Lowe's?
What's the law on lexan windows in a street car?
Lexan and Plexiglas are two differnt things. Lexan is stronger and more scratch resistant and won't shatter like Plexiglas will.
I believe that the law will change from state to state. Likely, few will allow it to be used as a windshield, though for side and rear windows you are likely ok (check with local laws first, I'm not paying your fines, nor doing your time 
).
Lexan still scratches like it's made of wax though, so you have to coat both sides with clear plastic film (basically tint without the tint).
Lexan is polycarbonate, and plexiglass is ussually acrylic. Polycarb is tough, and flexible (you can work it like sheetmetal), acrylic is weak, and brittle.
You can probably buy polycarbonate at Home Depot as well, if not then just hit the Yellow Pages under "plastics". I've done a few Lexan windows on Miatas - windshield, side and hardtop windows.
I can't comment on weight savings for a Civic, but going to 1/8" Lexan for a Miata hardtop window saves 5-6 lbs.
The law definitely varies from state to state. They're not street-legal in Colorado.
depending on what year your civic is i know flex-a-lite makes lexan (i believe it was lexan) windows for certain models.
you usually use lexan for weight savings in race cars. Its like fitting roll cages in street cars, unecessay, useless and possible dangerous(I'm not sure of lexan shatter strength compared to glass).
You want to save weight on a street car, try to get lighter wheels, remove some sound deadening... The guys here know all about weight savings, its all that they do.
cxhb wrote: depending on what year your civic is i know flex-a-lite makes lexan (i believe it was lexan) windows for certain models.
It's a 1977 1200. From what I've seen nobody makes anything for that car.
Flex-a-lite says 20-50 pounds saving. That's probably not enough to justify the money. For some reason I thought it would be more than that.
There's no reason to buy a Lexan/polycarbonate window. The stuff is really easy to work, and you can bend it to shape. Here's how to put it in a Miata hardtop: http://targamiata.com/tags.php?tag=lexan%20window . I've also installed vent windows that look completely stock until you tap on the glass, using the factory gaskets etc.
Note that even with the fairly tight bend on that window, I didn't need to heat or form the plastic in any way.
Lexan shatter strength is considerably higher than glass. As for why - well, it's a cheap way to save fairly significant weight. 20-50 lbs is significant to me, and I imagine it's a pretty high percentage of a 1977 Civic. I've also done it a few times to allow for extra venting. You can put a NACA duct in a plastic window easily, it's not so easy to do with glass. Same with exhaust vents on the rear window in a race car.
Yeah, the car only weighs about 1600 pounds stock.
Is Lexan tough? I've seen 1/4" lexan storefront door windows bounce back bricks, 1/2" will stop a .38 bullet from a short barrel revolver. No shattering, just a dent on the window. Had that video on tape for a long time. The .38 trick I did myself in the basement. Wifey was not happy.
If lexan is stronger than glass, why is is not allowed in some states?
You can save a few pounds, we saved 5-10 lbs on the 4 rear windows plus hardware for the two pop outs on our XR4Ti, we saved another 15 lbs by removing the sunroof/tray/mechanicals and riveting in a piece of Lexan. Luckily GA has no rules on vehicles including safety inspections even in the covered counties that have pollution controls (Atlanta Metro area). Other than passing smog you could be missing doors, windows, etc, though I'm sure a cop would pull you over and cite you for endangering the public :)
We used 3/8" and it's insanely strong, like we've beat it with hammers just for giggles after we riveted it in and it just bounces the hammer, same thing would have smashed the old windows. That being said they're prolly not used in cars cause it does scratch, it needs a UV protector layer which must face outwards or else it yellows, and while flexible it's hard to mold it to shape so if you wanted to install it on curved window surfaces you'd need a better way to adhere it than simple epoxy like normal shaped windows, like I said we had to rivet them in place...
So, I've confirmed that in Alabama you have to have a DOT approved windshield but you can use lexan for the other windows.
Some people say Lexan is unsafe because it is so strong that you can't break it in case of emergency. For example, if your roll your car the windows break out on their own, if you had to try and get your way out of the lexan you'd better be carrying a sawzall. That's why I always have a sawzall in the center console, you just never know. Safety first! 
Bryce
I use it on my front windshield of my racecar and went from oem weight of almost 100 pounds to 28 with 3/8" thickness. I have had it on since 2004. Newer lexan windows have good anti-scratch treatments that can keep them clear for awhile. Had mine made by clearonewindows.com...
what does nascar use ? is it the same stuff we can buy ?
That's why I always have a sawzall in the center console, you just never know. Safety first!
what ever happened to keeping some condoms in your center consol "to be safe"
Rojofro wrote: I use it on my front windshield of my racecar and went from oem weight of almost 100 pounds to 28 with 3/8" thickness. I have had it on since 2004. Newer lexan windows have good anti-scratch treatments that can keep them clear for awhile. Had mine made by clearonewindows.com...
Almost 100 lbs for a windshield? What do you race, a city bus? A stock Miata windshield is 22 lbs.
Keith, tell me more about putting polycarbonate side windows in. Did you use the regulators? Any trick to getting the window stiff enough so it doesnt pull out at the top at speed? What thickness did you use?
I looked on your web site but found no info on the side windows.
Thanks B
The side windows were on another car, one which was not obsessively documented online. Weird, I know. They were just the triangular vent windows in a Miata. Very simple and non-moving. Pull out old ones, trace shape, cut Lexan, insert NACA duct, reinstall.
But I've considered the moving side windows. I'd probably use the same thickness as the window glass so all the gaskets fit. On a frameless car like a Miata, they probably wouldn't be stiff enough. And they'd definitely scratch when you raised and lowered them. I don't think that's a situation where you'd end up with a functional improvement.
beaulieu wrote: what does nascar use ? is it the same stuff we can buy ?
Pretty much. We used to but the sheets tinted at Home Depot, though now they buy the windows molded to shape and plop them in like regular windows. Lexan is super easy to work with, but make sure you get the scratch resistant kind and leave the paper covering on until you are done cutting the windows. We used a regular jigsaw with a sheet metal blade amd cleaned up the edges with a file.
Does anyone make a turnkey front windshield for a miata? Got a 2004 miata race car looking for one....
Kendall
Granny's Speed Shop has Lexan window kits for RX 7's.
