So that's what I did yesterday, buy a thinner sheet of "lexan". Today I cut it to the same size. The 3/16" thick piece weighed 5.75 pounds. The 1/8" thick piece weighed 3.625 pounds.
Just about 2/3rds, as would be expected. It feels lighter than that, less than half the weight, but I guess that's an illusion.
I'm glad I bought lighter, even if it was another $25.
This doesn't matter anymore. While the orginal sheet by Sabic** had no UV protection, the new sheet by Palram (made in Kutztown, Pa, where my step-father taught school), called Palsun, has it on one side (and you can buy it with anti-UV on both sides).
SABIC Innovative Plastics (GE Plastics) who I think hold the own the word Lexan® , but loads of companies make the stuff.
It looks like I'd have to order this, and buy a whole sheet, 4x8' for $125. Even if money didn't matter, too much of a hurry to order it.
The girl who had 7 years experience selling plastic, told me that acryllic was still brittle, at the very least by comparison to lexan. I bought a quarter sheet anyhow, for $20. It was labeled green, but neither I nor the girl could see any color. The guy there did however, It was also labeled iirc 030:030 or something similar. Means green.