This likely won’t include anything novel for regulars but, this post on Core77 includes a pretty good explainer on cast vs. extruded acrylic, as well as the differences in Plexiglas / plexiglass nomenclature:
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In my limited experience:
- Cast engraves frosted, extruded engraves clear.
- Extruded smells more and worse when laser cut and engraved.
- Extruded often comes with a plastic backing. Cast comes with a brown paper backing. Neither of them cut well and both tend to create burn marks.
Note that Proofgrade acrylic is cast, then custom-masked with a backing that we find performs better.
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I have some cast that is plastic backed, it’s a scrap of .2" stuff I got from a local supplier. I rarely use it but love it when I do, and I’m not that far from running out. 
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what i appreciate about the GF masking is that it’s not such a @#*(&## PITA to remove, like the brown paper is. especially if it’s been on for a while. i have some old scraps my FIL got me nearly 3 years ago that i’ve only used some of because it’s just not worth the work of peeling masking off of some of it.
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My local plastics supplier just gave me 8 feet of 3/4 inch 6 inches wide because the masking was hard to remove. I just peeled it all off and remasked with new.
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We need a mnemonic to keep track. I alway forget which one is the stinky one (until it’s too late).
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Cast Can
Exclude Extrude
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Well, i can think of something else that is extruded and stinky, if that helps.
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Now I can’t un-see it. That works!
I suspected that might do the trick. 
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cast is the bast
extruded isn’t fit for fooded
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Sold ^
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Thanks guys! Now I’m not going to be able to remember that extruded acrylic is stinky without… 
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