can i cut high-impact polystyrene 1.5mm or 0.060 inch (vacu formed model airplanes) with a Sculpfun S9
Here’s a link to lahobbyguy.com and specifically a post about what materials are safe to burn.
https://lahobbyguy.com/bb/viewtopic.php?t=16
Here’s a snippet from that post
PolyStyrene Foam Catches fire. It catches fire quickly, burns rapidly, it melts, and only thin pieces cut. This is the #1 material that causes laser fires!
That last part makes me think a lot of people have tried. Otherwise, how could it be the number 1 material to cause fires? 
Use caution!
Probably not with a visible-light laser, unless the material is a dark opaque color. Transparent or light-colored plastics don’t absorb enough visible light to make anything happen.
The 10.6 µm IR light from a CO₂ laser cuts HIPS sheet like butter, although the stuff tends to get melty around the edges.