I've been happily cutting plywood (cheap) and acrylic (nice, but expensive). So I started searching for other things that I could safely cut, but at very little cost. The pound shop, or cheap stores like Ikea are often good sources of cheap things that can be re-purposed as raw material.

It seems that most plastics are OK to cut, with the exception of PVC which apparently gives of Hydrochloric Acid when it's cut which damages your machine, and yourself! So probably best to avoid PVC then!

So the question is, how to tell if something is PVC or not.
If it has a recycling triangle on it, then 3 or V in the middle indicates PCV. But the triangle scheme is completely voluntary, so not everything has it.

After some searching, I finally found this: isite.lps.org/gcooper/web/documents/IdentificationofPolymers.pdf by David A Katz. In his document, he details exactly how to identify a number of plastic type materials using very simple tests, all of which the home user should be able to carry out.

So now you have no excuse for killing yourself (or your neighbour depending how long your fume extraction pipe is) by accidentally cutting PVC!